diff --git a/lib/model/channel.dart b/lib/model/channel.dart
index a13e19cc18..4dbc61756e 100644
--- a/lib/model/channel.dart
+++ b/lib/model/channel.dart
@@ -1,3 +1,5 @@
+import 'dart:collection';
+
 import 'package:flutter/foundation.dart';
 
 import '../api/model/events.dart';
@@ -41,6 +43,8 @@ mixin ChannelStore {
   ///
   /// For policies directly applicable in the UI, see
   /// [isTopicVisibleInStream] and [isTopicVisible].
+  ///
+  /// Topics are treated case-insensitively; see [TopicName.isSameAs].
   UserTopicVisibilityPolicy topicVisibilityPolicy(int streamId, TopicName topic);
 
   /// The raw data structure underlying [topicVisibilityPolicy].
@@ -171,13 +175,13 @@ class ChannelStoreImpl with ChannelStore {
       streams.putIfAbsent(stream.streamId, () => stream);
     }
 
-    final topicVisibility = <int, Map<TopicName, UserTopicVisibilityPolicy>>{};
+    final topicVisibility = <int, TopicKeyedMap<UserTopicVisibilityPolicy>>{};
     for (final item in initialSnapshot.userTopics ?? const <UserTopicItem>[]) {
       if (_warnInvalidVisibilityPolicy(item.visibilityPolicy)) {
         // Not a value we expect. Keep it out of our data structures. // TODO(log)
         continue;
       }
-      final forStream = topicVisibility.putIfAbsent(item.streamId, () => {});
+      final forStream = topicVisibility.putIfAbsent(item.streamId, () => makeTopicKeyedMap());
       forStream[item.topicName] = item.visibilityPolicy;
     }
 
@@ -204,9 +208,9 @@ class ChannelStoreImpl with ChannelStore {
   final Map<int, Subscription> subscriptions;
 
   @override
-  Map<int, Map<TopicName, UserTopicVisibilityPolicy>> get debugTopicVisibility => topicVisibility;
+  Map<int, TopicKeyedMap<UserTopicVisibilityPolicy>> get debugTopicVisibility => topicVisibility;
 
-  final Map<int, Map<TopicName, UserTopicVisibilityPolicy>> topicVisibility;
+  final Map<int, TopicKeyedMap<UserTopicVisibilityPolicy>> topicVisibility;
 
   @override
   UserTopicVisibilityPolicy topicVisibilityPolicy(int streamId, TopicName topic) {
@@ -364,8 +368,26 @@ class ChannelStoreImpl with ChannelStore {
         topicVisibility.remove(event.streamId);
       }
     } else {
-      final forStream = topicVisibility.putIfAbsent(event.streamId, () => {});
+      final forStream = topicVisibility.putIfAbsent(event.streamId, () => makeTopicKeyedMap());
       forStream[event.topicName] = visibilityPolicy;
     }
   }
 }
+
+/// A [Map] with [TopicName] keys and [V] values.
+///
+/// When one of these is created by [makeTopicKeyedMap],
+/// key equality is done case-insensitively; see there.
+///
+/// This type should only be used for maps created by [makeTopicKeyedMap].
+/// It would be nice to enforce that.
+typedef TopicKeyedMap<V> = Map<TopicName, V>;
+
+/// Make a case-insensitive, case-preserving [TopicName]-keyed [LinkedHashMap].
+///
+/// The equality function is [TopicName.isSameAs],
+/// and the hash code is [String.hashCode] of [TopicName.canonicalize].
+TopicKeyedMap<V> makeTopicKeyedMap<V>() => LinkedHashMap<TopicName, V>(
+  equals: (a, b) => a.isSameAs(b),
+  hashCode: (k) => k.canonicalize().hashCode,
+);
diff --git a/lib/model/recent_senders.dart b/lib/model/recent_senders.dart
index a5c4bca778..f8b046641d 100644
--- a/lib/model/recent_senders.dart
+++ b/lib/model/recent_senders.dart
@@ -4,6 +4,7 @@ import 'package:flutter/foundation.dart';
 import '../api/model/events.dart';
 import '../api/model/model.dart';
 import 'algorithms.dart';
+import 'channel.dart';
 
 /// Tracks the latest messages sent by each user, in each stream and topic.
 ///
@@ -16,7 +17,7 @@ class RecentSenders {
 
   // topicSenders[streamId][topic][senderId] = MessageIdTracker
   @visibleForTesting
-  final Map<int, Map<TopicName, Map<int, MessageIdTracker>>> topicSenders = {};
+  final Map<int, TopicKeyedMap<Map<int, MessageIdTracker>>> topicSenders = {};
 
   /// The latest message the given user sent to the given stream,
   /// or null if no such message is known.
@@ -27,6 +28,8 @@ class RecentSenders {
 
   /// The latest message the given user sent to the given topic,
   /// or null if no such message is known.
+  ///
+  /// Topics are treated case-insensitively; see [TopicName.isSameAs].
   int? latestMessageIdOfSenderInTopic({
     required int streamId,
     required TopicName topic,
@@ -53,7 +56,7 @@ class RecentSenders {
     }
     for (final entry in messagesByUserInTopic.entries) {
       final (streamId, topic, senderId) = entry.key;
-      (((topicSenders[streamId] ??= {})[topic] ??= {})
+      (((topicSenders[streamId] ??= makeTopicKeyedMap())[topic] ??= {})
         [senderId] ??= MessageIdTracker()).addAll(entry.value);
     }
   }
@@ -64,7 +67,7 @@ class RecentSenders {
     final StreamMessage(:streamId, :topic, :senderId, id: int messageId) = message;
     ((streamSenders[streamId] ??= {})
       [senderId] ??= MessageIdTracker()).add(messageId);
-    (((topicSenders[streamId] ??= {})[topic] ??= {})
+    (((topicSenders[streamId] ??= makeTopicKeyedMap())[topic] ??= {})
       [senderId] ??= MessageIdTracker()).add(messageId);
   }
 
diff --git a/lib/model/unreads.dart b/lib/model/unreads.dart
index ad6b7b4b8d..e65197a980 100644
--- a/lib/model/unreads.dart
+++ b/lib/model/unreads.dart
@@ -41,14 +41,22 @@ class Unreads extends PerAccountStoreBase with ChangeNotifier {
     required CorePerAccountStore core,
     required ChannelStore channelStore,
   }) {
-    final streams = <int, Map<TopicName, QueueList<int>>>{};
+    final streams = <int, TopicKeyedMap<QueueList<int>>>{};
     final dms = <DmNarrow, QueueList<int>>{};
     final mentions = Set.of(initial.mentions);
 
     for (final unreadChannelSnapshot in initial.channels) {
       final streamId = unreadChannelSnapshot.streamId;
       final topic = unreadChannelSnapshot.topic;
-      (streams[streamId] ??= {})[topic] = QueueList.from(unreadChannelSnapshot.unreadMessageIds);
+      final topics = (streams[streamId] ??= makeTopicKeyedMap());
+      topics.update(topic,
+        // Older servers differentiate topics case-sensitively, but shouldn't:
+        //   https://github.com/zulip/zulip/pull/31869
+        // Our topic-keyed map is case-insensitive. When we've seen this
+        // topic before, modulo case, aggregate instead of clobbering.
+        // TODO(server-10) simplify away
+        (value) => setUnion(value, unreadChannelSnapshot.unreadMessageIds),
+        ifAbsent: () => QueueList.from(unreadChannelSnapshot.unreadMessageIds));
     }
 
     for (final unreadDmSnapshot in initial.dms) {
@@ -88,7 +96,10 @@ class Unreads extends PerAccountStoreBase with ChangeNotifier {
   // int count;
 
   /// Unread stream messages, as: stream ID → topic → message IDs (sorted).
-  final Map<int, Map<TopicName, QueueList<int>>> streams;
+  ///
+  /// The topic-keyed map is case-insensitive and case-preserving;
+  /// it comes from [makeTopicKeyedMap].
+  final Map<int, TopicKeyedMap<QueueList<int>>> streams;
 
   /// Unread DM messages, as: DM narrow → message IDs (sorted).
   final Map<DmNarrow, QueueList<int>> dms;
@@ -405,7 +416,7 @@ class Unreads extends PerAccountStoreBase with ChangeNotifier {
               _slowRemoveAllInDms(messageIdsSet);
             }
           case UpdateMessageFlagsRemoveEvent():
-            final newlyUnreadInStreams = <int, Map<TopicName, QueueList<int>>>{};
+            final newlyUnreadInStreams = <int, TopicKeyedMap<QueueList<int>>>{};
             final newlyUnreadInDms = <DmNarrow, QueueList<int>>{};
             for (final messageId in event.messages) {
               final detail = event.messageDetails![messageId];
@@ -420,7 +431,7 @@ class Unreads extends PerAccountStoreBase with ChangeNotifier {
               }
               switch (detail.type) {
                 case MessageType.stream:
-                  final topics = (newlyUnreadInStreams[detail.streamId!] ??= {});
+                  final topics = (newlyUnreadInStreams[detail.streamId!] ??= makeTopicKeyedMap());
                   final messageIds = (topics[detail.topic!] ??= QueueList());
                   messageIds.add(messageId);
                 case MessageType.direct:
@@ -488,14 +499,15 @@ class Unreads extends PerAccountStoreBase with ChangeNotifier {
   }
 
   void _addLastInStreamTopic(int messageId, int streamId, TopicName topic) {
-    ((streams[streamId] ??= {})[topic] ??= QueueList()).addLast(messageId);
+    ((streams[streamId] ??= makeTopicKeyedMap())[topic] ??= QueueList())
+      .addLast(messageId);
   }
 
   // [messageIds] must be sorted ascending and without duplicates.
   void _addAllInStreamTopic(QueueList<int> messageIds, int streamId, TopicName topic) {
     assert(messageIds.isNotEmpty);
     assert(isSortedWithoutDuplicates(messageIds));
-    final topics = streams[streamId] ??= {};
+    final topics = streams[streamId] ??= makeTopicKeyedMap();
     topics.update(topic,
       ifAbsent: () => messageIds,
       // setUnion dedupes existing and incoming unread IDs,
diff --git a/test/model/channel_test.dart b/test/model/channel_test.dart
index 5c00aca814..0fd83f64f9 100644
--- a/test/model/channel_test.dart
+++ b/test/model/channel_test.dart
@@ -1,4 +1,3 @@
-
 import 'package:checks/checks.dart';
 import 'package:test/scaffolding.dart';
 import 'package:zulip/api/model/events.dart';
@@ -7,7 +6,9 @@ import 'package:zulip/api/model/model.dart';
 import 'package:zulip/model/store.dart';
 import 'package:zulip/model/channel.dart';
 
+import '../api/model/model_checks.dart';
 import '../example_data.dart' as eg;
+import '../stdlib_checks.dart';
 import 'test_store.dart';
 
 void main() {
@@ -146,7 +147,7 @@ void main() {
 
       test('with nothing for topic', () async {
         final store = eg.store();
-        await store.addUserTopic(stream1, 'other topic', UserTopicVisibilityPolicy.muted);
+        await store.setUserTopic(stream1, 'other topic', UserTopicVisibilityPolicy.muted);
         check(store.topicVisibilityPolicy(stream1.streamId, eg.t('topic')))
           .equals(UserTopicVisibilityPolicy.none);
       });
@@ -158,9 +159,13 @@ void main() {
           UserTopicVisibilityPolicy.unmuted,
           UserTopicVisibilityPolicy.followed,
         ]) {
-          await store.addUserTopic(stream1, 'topic', policy);
+          await store.setUserTopic(stream1, 'topic', policy);
           check(store.topicVisibilityPolicy(stream1.streamId, eg.t('topic')))
             .equals(policy);
+
+          // Case-insensitive
+          check(store.topicVisibilityPolicy(stream1.streamId, eg.t('ToPiC')))
+            .equals(policy);
         }
       });
     });
@@ -193,27 +198,39 @@ void main() {
         final store = eg.store();
         await store.addStream(stream1);
         await store.addSubscription(eg.subscription(stream1));
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
         check(store.isTopicVisibleInStream(stream1.streamId, eg.t('topic'))).isFalse();
         check(store.isTopicVisible        (stream1.streamId, eg.t('topic'))).isFalse();
+
+        // Case-insensitive
+        check(store.isTopicVisibleInStream(stream1.streamId, eg.t('ToPiC'))).isFalse();
+        check(store.isTopicVisible        (stream1.streamId, eg.t('ToPiC'))).isFalse();
       });
 
       test('with policy unmuted', () async {
         final store = eg.store();
         await store.addStream(stream1);
         await store.addSubscription(eg.subscription(stream1, isMuted: true));
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.unmuted);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.unmuted);
         check(store.isTopicVisibleInStream(stream1.streamId, eg.t('topic'))).isTrue();
         check(store.isTopicVisible        (stream1.streamId, eg.t('topic'))).isTrue();
+
+        // Case-insensitive
+        check(store.isTopicVisibleInStream(stream1.streamId, eg.t('tOpIc'))).isTrue();
+        check(store.isTopicVisible        (stream1.streamId, eg.t('tOpIc'))).isTrue();
       });
 
       test('with policy followed', () async {
         final store = eg.store();
         await store.addStream(stream1);
         await store.addSubscription(eg.subscription(stream1, isMuted: true));
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.followed);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.followed);
         check(store.isTopicVisibleInStream(stream1.streamId, eg.t('topic'))).isTrue();
         check(store.isTopicVisible        (stream1.streamId, eg.t('topic'))).isTrue();
+
+        // Case-insensitive
+        check(store.isTopicVisibleInStream(stream1.streamId, eg.t('TOPIC'))).isTrue();
+        check(store.isTopicVisible        (stream1.streamId, eg.t('TOPIC'))).isTrue();
       });
     });
 
@@ -221,6 +238,18 @@ void main() {
       UserTopicEvent mkEvent(UserTopicVisibilityPolicy policy) =>
         eg.userTopicEvent(stream1.streamId, 'topic', policy);
 
+      // For testing case-insensitivity
+      UserTopicEvent mkEventDifferentlyCased(UserTopicVisibilityPolicy policy) =>
+        eg.userTopicEvent(stream1.streamId, 'ToPiC', policy);
+
+      assert(() {
+        // (sanity check on mkEvent and mkEventDifferentlyCased)
+        final event1 = mkEvent(UserTopicVisibilityPolicy.followed);
+        final event2 = mkEventDifferentlyCased(UserTopicVisibilityPolicy.followed);
+        return event1.topicName.isSameAs(event2.topicName)
+          && event1.topicName.apiName != event2.topicName.apiName;
+      }());
+
       void checkChanges(PerAccountStore store,
           UserTopicVisibilityPolicy newPolicy,
           UserTopicVisibilityEffect expectedInStream,
@@ -228,6 +257,10 @@ void main() {
         final event = mkEvent(newPolicy);
         check(store.willChangeIfTopicVisibleInStream(event)).equals(expectedInStream);
         check(store.willChangeIfTopicVisible        (event)).equals(expectedOverall);
+
+        final event2 = mkEventDifferentlyCased(newPolicy);
+        check(store.willChangeIfTopicVisibleInStream(event2)).equals(expectedInStream);
+        check(store.willChangeIfTopicVisible        (event2)).equals(expectedOverall);
       }
 
       test('stream not muted, policy none -> followed, no change', () async {
@@ -341,7 +374,7 @@ void main() {
     group('events', () {
       test('add with new stream', () async {
         final store = eg.store();
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
         compareTopicVisibility(store, [
           eg.userTopicItem(stream1, 'topic', UserTopicVisibilityPolicy.muted),
         ]);
@@ -349,8 +382,8 @@ void main() {
 
       test('add in existing stream', () async {
         final store = eg.store();
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
-        await store.addUserTopic(stream1, 'other topic', UserTopicVisibilityPolicy.unmuted);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
+        await store.setUserTopic(stream1, 'other topic', UserTopicVisibilityPolicy.unmuted);
         compareTopicVisibility(store, [
           eg.userTopicItem(stream1, 'topic', UserTopicVisibilityPolicy.muted),
           eg.userTopicItem(stream1, 'other topic', UserTopicVisibilityPolicy.unmuted),
@@ -359,18 +392,24 @@ void main() {
 
       test('update existing policy', () async {
         final store = eg.store();
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.unmuted);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.unmuted);
         compareTopicVisibility(store, [
           eg.userTopicItem(stream1, 'topic', UserTopicVisibilityPolicy.unmuted),
         ]);
+
+        // case-insensitivity
+        await store.setUserTopic(stream1, 'ToPiC', UserTopicVisibilityPolicy.followed);
+        compareTopicVisibility(store, [
+          eg.userTopicItem(stream1, 'topic', UserTopicVisibilityPolicy.followed),
+        ]);
       });
 
       test('remove, with others in stream', () async {
         final store = eg.store();
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
-        await store.addUserTopic(stream1, 'other topic', UserTopicVisibilityPolicy.unmuted);
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.none);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
+        await store.setUserTopic(stream1, 'other topic', UserTopicVisibilityPolicy.unmuted);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.none);
         compareTopicVisibility(store, [
           eg.userTopicItem(stream1, 'other topic', UserTopicVisibilityPolicy.unmuted),
         ]);
@@ -378,16 +417,18 @@ void main() {
 
       test('remove, as last in stream', () async {
         final store = eg.store();
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.none);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
+        // case-insensitivity
+        await store.setUserTopic(stream1, 'ToPiC', UserTopicVisibilityPolicy.none);
         compareTopicVisibility(store, [
         ]);
       });
 
       test('treat unknown enum value as removing', () async {
         final store = eg.store();
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
-        await store.addUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.unknown);
+        await store.setUserTopic(stream1, 'topic', UserTopicVisibilityPolicy.muted);
+        // case-insensitivity
+        await store.setUserTopic(stream1, 'ToPiC', UserTopicVisibilityPolicy.unknown);
         compareTopicVisibility(store, [
         ]);
       });
@@ -404,7 +445,8 @@ void main() {
         ]));
       check(store.topicVisibilityPolicy(stream.streamId, eg.t('topic 1')))
         .equals(UserTopicVisibilityPolicy.muted);
-      check(store.topicVisibilityPolicy(stream.streamId, eg.t('topic 2')))
+      // case-insensitivity
+      check(store.topicVisibilityPolicy(stream.streamId, eg.t('ToPiC 2')))
         .equals(UserTopicVisibilityPolicy.unmuted);
       check(store.topicVisibilityPolicy(stream.streamId, eg.t('topic 3')))
         .equals(UserTopicVisibilityPolicy.followed);
@@ -412,4 +454,30 @@ void main() {
         .equals(UserTopicVisibilityPolicy.none);
     });
   });
+
+  group('makeTopicKeyedMap', () {
+    test('"a" equals "A"', () {
+      final map = makeTopicKeyedMap<int>()
+        ..[eg.t('a')] = 1
+        ..[eg.t('A')] = 2;
+      check(map)
+        ..[eg.t('a')].equals(2)
+        ..[eg.t('A')].equals(2)
+        ..entries.which((it) => it.single
+          ..key.apiName.equals('a')
+          ..value.equals(2));
+    });
+
+    test('"A" equals "a"', () {
+      final map = makeTopicKeyedMap<int>()
+        ..[eg.t('A')] = 1
+        ..[eg.t('a')] = 2;
+      check(map)
+        ..[eg.t('A')].equals(2)
+        ..[eg.t('a')].equals(2)
+        ..entries.which((it) => it.single
+          ..key.apiName.equals('A')
+          ..value.equals(2));
+    });
+  });
 }
diff --git a/test/model/message_list_test.dart b/test/model/message_list_test.dart
index 0779af52a1..dbe2e6d8eb 100644
--- a/test/model/message_list_test.dart
+++ b/test/model/message_list_test.dart
@@ -359,7 +359,7 @@ void main() {
       final stream = eg.stream();
       final otherStream = eg.stream();
       await prepare(narrow: ChannelNarrow(stream.streamId));
-      await store.addUserTopic(stream, 'muted', UserTopicVisibilityPolicy.muted);
+      await store.setUserTopic(stream, 'muted', UserTopicVisibilityPolicy.muted);
       await prepareOutboxMessagesTo([
         StreamDestination(stream.streamId, eg.t('topic')),
         StreamDestination(stream.streamId, eg.t('muted')),
@@ -1124,7 +1124,7 @@ void main() {
         eg.streamMessage(id: 2, stream: stream, topic: topic),
       ];
       await prepareMessages(foundOldest: true, messages: messages);
-      await store.addUserTopic(stream, 'muted', UserTopicVisibilityPolicy.muted);
+      await store.setUserTopic(stream, 'muted', UserTopicVisibilityPolicy.muted);
       await prepareOutboxMessagesTo([
         StreamDestination(stream.streamId, eg.t(topic)),
         StreamDestination(stream.streamId, eg.t('muted')),
@@ -2218,9 +2218,9 @@ void main() {
       await prepare(narrow: const CombinedFeedNarrow());
       await store.addStreams([stream1, stream2]);
       await store.addSubscription(eg.subscription(stream1));
-      await store.addUserTopic(stream1, 'B', UserTopicVisibilityPolicy.muted);
+      await store.setUserTopic(stream1, 'B', UserTopicVisibilityPolicy.muted);
       await store.addSubscription(eg.subscription(stream2, isMuted: true));
-      await store.addUserTopic(stream2, 'C', UserTopicVisibilityPolicy.unmuted);
+      await store.setUserTopic(stream2, 'C', UserTopicVisibilityPolicy.unmuted);
 
       // Check filtering on fetchInitial…
       await prepareMessages(foundOldest: false, messages: [
@@ -2278,8 +2278,8 @@ void main() {
       await prepare(narrow: ChannelNarrow(stream.streamId));
       await store.addStream(stream);
       await store.addSubscription(eg.subscription(stream, isMuted: true));
-      await store.addUserTopic(stream, 'A', UserTopicVisibilityPolicy.unmuted);
-      await store.addUserTopic(stream, 'C', UserTopicVisibilityPolicy.muted);
+      await store.setUserTopic(stream, 'A', UserTopicVisibilityPolicy.unmuted);
+      await store.setUserTopic(stream, 'C', UserTopicVisibilityPolicy.muted);
 
       // Check filtering on fetchInitial…
       await prepareMessages(foundOldest: false, messages: [
@@ -2323,7 +2323,7 @@ void main() {
       await prepare(narrow: ChannelNarrow(stream.streamId));
       await store.addStream(stream);
       await store.addSubscription(eg.subscription(stream));
-      await store.addUserTopic(stream, 'muted', UserTopicVisibilityPolicy.muted);
+      await store.setUserTopic(stream, 'muted', UserTopicVisibilityPolicy.muted);
       await prepareMessages(foundOldest: true, messages: []);
 
       // Check filtering on sent messages…
@@ -2356,7 +2356,7 @@ void main() {
       await prepare(narrow: eg.topicNarrow(stream.streamId, 'A'));
       await store.addStream(stream);
       await store.addSubscription(eg.subscription(stream, isMuted: true));
-      await store.addUserTopic(stream, 'A', UserTopicVisibilityPolicy.muted);
+      await store.setUserTopic(stream, 'A', UserTopicVisibilityPolicy.muted);
 
       // Check filtering on fetchInitial…
       await prepareMessages(foundOldest: false, messages: [
@@ -2386,7 +2386,7 @@ void main() {
       const mutedTopic = 'muted';
       await prepare(narrow: const MentionsNarrow());
       await store.addStream(stream);
-      await store.addUserTopic(stream, mutedTopic, UserTopicVisibilityPolicy.muted);
+      await store.setUserTopic(stream, mutedTopic, UserTopicVisibilityPolicy.muted);
       await store.addSubscription(eg.subscription(stream, isMuted: true));
 
       List<Message> getMessages(int startingId) => [
@@ -2424,7 +2424,7 @@ void main() {
       const mutedTopic = 'muted';
       await prepare(narrow: const StarredMessagesNarrow());
       await store.addStream(stream);
-      await store.addUserTopic(stream, mutedTopic, UserTopicVisibilityPolicy.muted);
+      await store.setUserTopic(stream, mutedTopic, UserTopicVisibilityPolicy.muted);
       await store.addSubscription(eg.subscription(stream, isMuted: true));
 
       List<Message> getMessages(int startingId) => [
diff --git a/test/model/recent_senders_test.dart b/test/model/recent_senders_test.dart
index 602362cbcc..990811d216 100644
--- a/test/model/recent_senders_test.dart
+++ b/test/model/recent_senders_test.dart
@@ -1,13 +1,16 @@
 import 'package:checks/checks.dart';
+import 'package:collection/collection.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:zulip/api/model/events.dart';
 import 'package:zulip/api/model/model.dart';
+import 'package:zulip/model/channel.dart';
 import 'package:zulip/model/recent_senders.dart';
 import '../example_data.dart' as eg;
 
 /// [messages] should be sorted by [id] ascending.
 void checkMatchesMessages(RecentSenders model, List<Message> messages) {
   final Map<int, Map<int, Set<int>>> messagesByUserInStream = {};
-  final Map<int, Map<TopicName, Map<int, Set<int>>>> messagesByUserInTopic = {};
+  final Map<int, TopicKeyedMap<Map<int, Set<int>>>> messagesByUserInTopic = {};
   for (final message in messages) {
     if (message is! StreamMessage) {
       throw UnsupportedError('Message of type ${message.runtimeType} is not expected.');
@@ -17,7 +20,7 @@ void checkMatchesMessages(RecentSenders model, List<Message> messages) {
 
     ((messagesByUserInStream[streamId] ??= {})
       [senderId] ??= {}).add(messageId);
-    (((messagesByUserInTopic[streamId] ??= {})[topic] ??= {})
+    (((messagesByUserInTopic[streamId] ??= makeTopicKeyedMap())[topic] ??= {})
       [senderId] ??= {}).add(messageId);
   }
 
@@ -125,6 +128,16 @@ void main() {
         [eg.streamMessage(stream: streamA, topic: 'other', sender: userX)]);
     });
 
+    test('case-insensitive topics', () {
+      checkHandleMessages(
+        [eg.streamMessage(stream: streamA, topic: 'thing', sender: userX)],
+        [eg.streamMessage(stream: streamA, topic: 'ThInG', sender: userX)]);
+      check(model.topicSenders).values.single.deepEquals(
+        {eg.t('thing'):
+          {userX.userId: (Subject<Object?> it) =>
+             it.isA<MessageIdTracker>().ids.length.equals(2)}});
+    });
+
     test('add new stream', () {
       checkHandleMessages(
         [eg.streamMessage(stream: streamA, topic: 'thing', sender: userX)],
@@ -161,6 +174,16 @@ void main() {
       Map.fromEntries(messages.map((msg) => MapEntry(msg.id, msg))));
 
     checkMatchesMessages(model, [messages[1]]);
+
+    // check case-insensitivity
+    model.handleDeleteMessageEvent(DeleteMessageEvent(
+      id: 0,
+      messageIds: [messages[1].id],
+      messageType: MessageType.stream,
+      streamId: stream.streamId,
+      topic: eg.t('oThEr'),
+    ), {messages[1].id: messages[1]});
+    checkMatchesMessages(model, []);
   });
 
   test('RecentSenders.latestMessageIdOfSenderInStream', () {
@@ -200,6 +223,9 @@ void main() {
 
     check(model.latestMessageIdOfSenderInTopic(streamId: 1,
       topic: eg.t('a'), senderId: 10)).equals(300);
+    // case-insensitivity
+    check(model.latestMessageIdOfSenderInTopic(streamId: 1,
+      topic: eg.t('A'), senderId: 10)).equals(300);
     // No message of user 20 in topic "a".
     check(model.latestMessageIdOfSenderInTopic(streamId: 1,
       topic: eg.t('a'), senderId: 20)).equals(null);
@@ -211,3 +237,7 @@ void main() {
       topic: eg.t('a'), senderId: 10)).equals(null);
   });
 }
+
+extension MessageIdTrackerChecks on Subject<MessageIdTracker> {
+  Subject<QueueList<int>> get ids => has((x) => x.ids, 'ids');
+}
diff --git a/test/model/test_store.dart b/test/model/test_store.dart
index d979e737f9..1d086d4290 100644
--- a/test/model/test_store.dart
+++ b/test/model/test_store.dart
@@ -287,7 +287,7 @@ extension PerAccountStoreTestExtension on PerAccountStore {
     await handleEvent(SubscriptionAddEvent(id: 1, subscriptions: subscriptions));
   }
 
-  Future<void> addUserTopic(ZulipStream stream, String topic, UserTopicVisibilityPolicy visibilityPolicy) async {
+  Future<void> setUserTopic(ZulipStream stream, String topic, UserTopicVisibilityPolicy visibilityPolicy) async {
     await handleEvent(eg.userTopicEvent(stream.streamId, topic, visibilityPolicy));
   }
 
diff --git a/test/model/unreads_test.dart b/test/model/unreads_test.dart
index de554b220c..e1c5ca6986 100644
--- a/test/model/unreads_test.dart
+++ b/test/model/unreads_test.dart
@@ -4,14 +4,29 @@ import 'package:test/scaffolding.dart';
 import 'package:zulip/api/model/events.dart';
 import 'package:zulip/api/model/initial_snapshot.dart';
 import 'package:zulip/api/model/model.dart';
+import 'package:zulip/model/algorithms.dart';
+import 'package:zulip/model/channel.dart';
 import 'package:zulip/model/narrow.dart';
 import 'package:zulip/model/store.dart';
 import 'package:zulip/model/unreads.dart';
 
 import '../example_data.dart' as eg;
+import '../stdlib_checks.dart';
 import 'test_store.dart';
 import 'unreads_checks.dart';
 
+void checkInvariants(Unreads model) {
+  for (final MapEntry(value: topics) in model.streams.entries) {
+    for (final MapEntry(value: messageIds) in topics.entries) {
+      check(isSortedWithoutDuplicates(messageIds)).isTrue();
+    }
+  }
+
+  for (final MapEntry(value: messageIds) in model.dms.entries) {
+    check(isSortedWithoutDuplicates(messageIds)).isTrue();
+  }
+}
+
 void main() {
   // These variables are the common state operated on by each test.
   // Each test case calls [prepare] to initialize them.
@@ -23,7 +38,10 @@ void main() {
     check(notifiedCount).equals(count);
     notifiedCount = 0;
   }
-  void checkNotNotified() => checkNotified(count: 0);
+  void checkNotNotified() {
+    checkInvariants(model);
+    checkNotified(count: 0);
+  }
   void checkNotifiedOnce() => checkNotified(count: 1);
 
   /// Initialize [model] and the rest of the test state.
@@ -38,15 +56,18 @@ void main() {
     ),
   }) {
     store = eg.store(initialSnapshot: eg.initialSnapshot(unreadMsgs: initial));
+    checkInvariants(store.unreads);
     notifiedCount = 0;
     model = store.unreads
       ..addListener(() {
+        checkInvariants(model);
         notifiedCount++;
       });
     checkNotNotified();
   }
 
-  void fillWithMessages(Iterable<Message> messages) {
+  void fillWithMessages(List<Message> messages) {
+    check(isSortedWithoutDuplicates(messages.map((m) => m.id).toList())).isTrue();
     for (final message in messages) {
       model.handleMessageEvent(eg.messageEvent(message));
     }
@@ -57,7 +78,7 @@ void main() {
     assert(Set.of(messages.map((m) => m.id)).length == messages.length,
       'checkMatchesMessages: duplicate messages in test input');
 
-    final Map<int, Map<TopicName, QueueList<int>>> expectedStreams = {};
+    final Map<int, TopicKeyedMap<QueueList<int>>> expectedStreams = {};
     final Map<DmNarrow, QueueList<int>> expectedDms = {};
     final Set<int> expectedMentions = {};
     for (final message in messages) {
@@ -66,7 +87,7 @@ void main() {
       }
       switch (message) {
         case StreamMessage():
-          final perTopic = expectedStreams[message.streamId] ??= {};
+          final perTopic = expectedStreams[message.streamId] ??= makeTopicKeyedMap();
           final messageIds = perTopic[message.topic] ??= QueueList();
           messageIds.add(message.id);
         case DmMessage():
@@ -117,16 +138,19 @@ void main() {
           eg.unreadChannelMsgs(streamId: stream1.streamId, topic: 'b', unreadMessageIds: [3, 4]),
           eg.unreadChannelMsgs(streamId: stream2.streamId, topic: 'b', unreadMessageIds: [5, 6]),
           eg.unreadChannelMsgs(streamId: stream2.streamId, topic: 'c', unreadMessageIds: [7, 8]),
+
+          // TODO(server-10) drop this (see implementation)
+          eg.unreadChannelMsgs(streamId: stream2.streamId, topic: 'C', unreadMessageIds: [9, 10]),
         ],
         dms: [
-          UnreadDmSnapshot(otherUserId: 1, unreadMessageIds: [9, 10]),
-          UnreadDmSnapshot(otherUserId: 2, unreadMessageIds: [11, 12]),
+          UnreadDmSnapshot(otherUserId: 1, unreadMessageIds: [11, 12]),
+          UnreadDmSnapshot(otherUserId: 2, unreadMessageIds: [13, 14]),
         ],
         huddles: [
-          UnreadHuddleSnapshot(userIdsString: '1,2,${eg.selfUser.userId}', unreadMessageIds: [13, 14]),
-          UnreadHuddleSnapshot(userIdsString: '2,3,${eg.selfUser.userId}', unreadMessageIds: [15, 16]),
+          UnreadHuddleSnapshot(userIdsString: '1,2,${eg.selfUser.userId}', unreadMessageIds: [15, 16]),
+          UnreadHuddleSnapshot(userIdsString: '2,3,${eg.selfUser.userId}', unreadMessageIds: [17, 18]),
         ],
-        mentions: [6, 12, 16],
+        mentions: [6, 14, 18],
         oldUnreadsMissing: false,
       ));
       checkMatchesMessages([
@@ -138,14 +162,16 @@ void main() {
         eg.streamMessage(id: 6, stream: stream2, topic: 'b', flags: [MessageFlag.mentioned]),
         eg.streamMessage(id: 7, stream: stream2, topic: 'c', flags: []),
         eg.streamMessage(id: 8, stream: stream2, topic: 'c', flags: []),
-        eg.dmMessage(id: 9,  from: user1, to: [eg.selfUser], flags: []),
-        eg.dmMessage(id: 10, from: user1, to: [eg.selfUser], flags: []),
-        eg.dmMessage(id: 11, from: user2, to: [eg.selfUser], flags: []),
-        eg.dmMessage(id: 12, from: user2, to: [eg.selfUser], flags: [MessageFlag.mentioned]),
-        eg.dmMessage(id: 13, from: user1, to: [user2, eg.selfUser], flags: []),
-        eg.dmMessage(id: 14, from: user1, to: [user2, eg.selfUser], flags: []),
-        eg.dmMessage(id: 15, from: user2, to: [user3, eg.selfUser], flags: []),
-        eg.dmMessage(id: 16, from: user2, to: [user3, eg.selfUser], flags: [MessageFlag.wildcardMentioned]),
+        eg.streamMessage(id: 9, stream: stream2, topic: 'C', flags: []),
+        eg.streamMessage(id: 10, stream: stream2, topic: 'C', flags: []),
+        eg.dmMessage(id: 11,  from: user1, to: [eg.selfUser], flags: []),
+        eg.dmMessage(id: 12, from: user1, to: [eg.selfUser], flags: []),
+        eg.dmMessage(id: 13, from: user2, to: [eg.selfUser], flags: []),
+        eg.dmMessage(id: 14, from: user2, to: [eg.selfUser], flags: [MessageFlag.mentioned]),
+        eg.dmMessage(id: 15, from: user1, to: [user2, eg.selfUser], flags: []),
+        eg.dmMessage(id: 16, from: user1, to: [user2, eg.selfUser], flags: []),
+        eg.dmMessage(id: 17, from: user2, to: [user3, eg.selfUser], flags: []),
+        eg.dmMessage(id: 18, from: user2, to: [user3, eg.selfUser], flags: [MessageFlag.wildcardMentioned]),
       ]);
     });
   });
@@ -160,7 +186,7 @@ void main() {
       await store.addSubscription(eg.subscription(stream1));
       await store.addSubscription(eg.subscription(stream2));
       await store.addSubscription(eg.subscription(stream3, isMuted: true));
-      await store.addUserTopic(stream1, 'a', UserTopicVisibilityPolicy.muted);
+      await store.setUserTopic(stream1, 'a', UserTopicVisibilityPolicy.muted);
       fillWithMessages([
         eg.streamMessage(stream: stream1, topic: 'a', flags: []),
         eg.streamMessage(stream: stream1, topic: 'b', flags: []),
@@ -178,14 +204,14 @@ void main() {
       prepare();
       await store.addStream(stream);
       await store.addSubscription(eg.subscription(stream));
-      await store.addUserTopic(stream, 'a', UserTopicVisibilityPolicy.unmuted);
-      await store.addUserTopic(stream, 'c', UserTopicVisibilityPolicy.muted);
+      await store.setUserTopic(stream, 'a', UserTopicVisibilityPolicy.unmuted);
+      await store.setUserTopic(stream, 'c', UserTopicVisibilityPolicy.muted);
       fillWithMessages([
         eg.streamMessage(stream: stream, topic: 'a', flags: []),
-        eg.streamMessage(stream: stream, topic: 'a', flags: []),
-        eg.streamMessage(stream: stream, topic: 'b', flags: []),
+        eg.streamMessage(stream: stream, topic: 'A', flags: []),
         eg.streamMessage(stream: stream, topic: 'b', flags: []),
         eg.streamMessage(stream: stream, topic: 'b', flags: []),
+        eg.streamMessage(stream: stream, topic: 'B', flags: []),
         eg.streamMessage(stream: stream, topic: 'c', flags: []),
       ]);
       check(model.countInChannel      (stream.streamId)).equals(5);
@@ -201,9 +227,13 @@ void main() {
     test('countInTopicNarrow', () {
       final stream = eg.stream();
       prepare();
-      fillWithMessages(List.generate(7, (i) => eg.streamMessage(
-        stream: stream, topic: 'a', flags: [])));
-      check(model.countInTopicNarrow(stream.streamId, eg.t('a'))).equals(7);
+      final messages = [
+        ...List.generate(7, (i) => eg.streamMessage(stream: stream, topic: 'a', flags: [])),
+        ...List.generate(2, (i) => eg.streamMessage(stream: stream, topic: 'A', flags: [])),
+      ];
+      fillWithMessages(messages);
+      check(model.countInTopicNarrow(stream.streamId, eg.t('a'))).equals(9);
+      check(model.countInTopicNarrow(stream.streamId, eg.t('A'))).equals(9);
     });
 
     test('countInDmNarrow', () {
@@ -242,9 +272,9 @@ void main() {
   group('isUnread', () {
     final unreadDmMessage = eg.dmMessage(
       from: eg.otherUser, to: [eg.selfUser], flags: []);
+    final unreadChannelMessage = eg.streamMessage(flags: []);
     final readDmMessage = eg.dmMessage(
       from: eg.otherUser, to: [eg.selfUser], flags: [MessageFlag.read]);
-    final unreadChannelMessage = eg.streamMessage(flags: []);
     final readChannelMessage = eg.streamMessage(flags: [MessageFlag.read]);
 
     final allMessages = <Message>[
@@ -351,6 +381,24 @@ void main() {
           });
         }
       });
+
+      test('topics case-insensitive but case-preserving', () {
+        final stream = eg.stream();
+        final message1 = eg.streamMessage(stream: stream, topic: 'aaa');
+        final message2 = eg.streamMessage(stream: stream, topic: 'AaA');
+        final message3 = eg.streamMessage(stream: stream, topic: 'aAa');
+        prepare();
+        fillWithMessages([message1]);
+        model.handleMessageEvent(eg.messageEvent(message2));
+        model.handleMessageEvent(eg.messageEvent(message3));
+        checkNotified(count: 2);
+        checkMatchesMessages([message1, message2, message3]);
+        // Redundant with checkMatchesMessages, but for explicitness here:
+        check(model).streams.values.single
+          .entries.single
+            ..key.equals(eg.t('aaa'))
+            ..value.length.equals(3);
+      });
     });
 
     group('DM messages', () {
@@ -481,11 +529,11 @@ void main() {
         prepare();
         await store.addStream(origChannel);
         await store.addSubscription(eg.subscription(origChannel));
+        unreadMessages = List<StreamMessage>.generate(10,
+          (_) => eg.streamMessage(stream: origChannel, topic: origTopic));
         readMessages  = List<StreamMessage>.generate(10,
           (_) => eg.streamMessage(stream: origChannel, topic: origTopic,
                    flags: [MessageFlag.read]));
-        unreadMessages = List<StreamMessage>.generate(10,
-          (_) => eg.streamMessage(stream: origChannel, topic: origTopic));
       }
 
       List<StreamMessage> copyMessagesWith(Iterable<StreamMessage> messages, {
@@ -600,17 +648,49 @@ void main() {
       test('tolerates unsorted messages', () async {
         await prepareStore();
         final unreadMessages = List.generate(10, (i) =>
-          eg.streamMessage(
-            id: 1000 - i, stream: origChannel, topic: origTopic));
+          eg.streamMessage(stream: origChannel, topic: origTopic));
         fillWithMessages(unreadMessages);
 
         model.handleUpdateMessageEvent(eg.updateMessageEventMoveFrom(
-          origMessages: unreadMessages,
+          origMessages: unreadMessages.reversed.toList(),
           newTopicStr: newTopic));
         checkNotifiedOnce();
         checkMatchesMessages(copyMessagesWith(unreadMessages, newTopic: newTopic));
       });
 
+      test('topics case-insensitive but case-preserving', () async {
+        final message1 = eg.streamMessage(stream: origChannel, topic: 'aaa', flags: []);
+        final message2 = eg.streamMessage(stream: origChannel, topic: 'aaa', flags: []);
+        final messages = [message1, message2];
+        await prepareStore();
+        fillWithMessages(messages);
+
+        model.handleUpdateMessageEvent(eg.updateMessageEventMoveFrom(
+          // 'AAA' finds the key 'aaa'
+          origMessages: copyMessagesWith([message1], newTopic: 'AAA'),
+          newTopicStr: 'bbb'));
+        checkNotifiedOnce();
+        checkMatchesMessages([
+          ...copyMessagesWith([message1], newTopic: 'bbb'),
+          message2,
+        ]);
+
+        model.handleUpdateMessageEvent(eg.updateMessageEventMoveFrom(
+          origMessages: [message2],
+          // 'BBB' finds the key 'bbb'
+          newTopicStr: 'BBB'));
+        checkNotifiedOnce();
+        checkMatchesMessages([
+          ...copyMessagesWith([message1], newTopic: 'bbb'),
+          ...copyMessagesWith([message2], newTopic: 'BBB'),
+        ]);
+        // Redundant with checkMatchesMessages, but for explicitness here:
+        check(model).streams.values.single
+          .entries.single
+            ..key.equals(eg.t('bbb'))
+            ..value.length.equals(2);
+      });
+
       test('tolerates unreads unknown to the model', () async {
         await prepareStore();
         fillWithMessages(unreadMessages);
@@ -672,6 +752,7 @@ void main() {
       fillWithMessages(messages);
 
       final expectedRemainingMessages = Set.of(messages);
+      assert(messages.any((m) => m.id == 14));
       for (final message in messages) {
         final event = switch (message) {
           StreamMessage() => DeleteMessageEvent(
@@ -679,7 +760,12 @@ void main() {
             messageType: MessageType.stream,
             messageIds: [message.id],
             streamId: message.streamId,
-            topic: message.topic,
+            topic: () {
+              if (message.id != 14) return message.topic;
+              final uppercase = message.topic.apiName.toUpperCase();
+              assert(message.topic.apiName != uppercase);
+              return eg.t(uppercase); // exercise case-insensitivity of topics
+            }(),
           ),
           DmMessage() => DeleteMessageEvent(
             id: 0,
diff --git a/test/stdlib_checks.dart b/test/stdlib_checks.dart
index 8bfaea54fd..28b5f5e5f2 100644
--- a/test/stdlib_checks.dart
+++ b/test/stdlib_checks.dart
@@ -16,6 +16,11 @@ extension ListChecks<T> on Subject<List<T>> {
   Subject<T> operator [](int index) => has((l) => l[index], '[$index]');
 }
 
+extension MapEntryChecks<K, V> on Subject<MapEntry<K, V>> {
+  Subject<K> get key => has((e) => e.key, 'key');
+  Subject<V> get value => has((e) => e.value, 'value');
+}
+
 extension NullableMapChecks<K, V> on Subject<Map<K, V>?> {
   void deepEquals(Map<Object?, Object?>? expected) {
     if (expected == null) {
diff --git a/test/widgets/inbox_test.dart b/test/widgets/inbox_test.dart
index 4d24e5d831..fe96b427ab 100644
--- a/test/widgets/inbox_test.dart
+++ b/test/widgets/inbox_test.dart
@@ -9,6 +9,7 @@ import 'package:zulip/widgets/color.dart';
 import 'package:zulip/widgets/home.dart';
 import 'package:zulip/widgets/icons.dart';
 import 'package:zulip/widgets/channel_colors.dart';
+import 'package:zulip/widgets/unread_count_badge.dart';
 
 import '../example_data.dart' as eg;
 import '../flutter_checks.dart';
@@ -58,6 +59,7 @@ void main() {
     List<Subscription>? subscriptions,
     List<User>? users,
     required List<Message> unreadMessages,
+    List<Message>? otherMessages,
     NavigatorObserver? navigatorObserver,
   }) async {
     addTearDown(testBinding.reset);
@@ -227,7 +229,7 @@ void main() {
           streams: [stream],
           subscriptions: [subscription],
           unreadMessages: [eg.streamMessage(stream: stream, topic: 'lunch')]);
-        await store.addUserTopic(stream, 'lunch', UserTopicVisibilityPolicy.muted);
+        await store.setUserTopic(stream, 'lunch', UserTopicVisibilityPolicy.muted);
         await tester.pump();
         check(tester.widgetList(find.text('lunch'))).length.equals(0);
       });
@@ -249,7 +251,7 @@ void main() {
           streams: [stream],
           subscriptions: [subscription],
           unreadMessages: [eg.streamMessage(stream: stream, topic: 'lunch')]);
-        await store.addUserTopic(stream, 'lunch', UserTopicVisibilityPolicy.unmuted);
+        await store.setUserTopic(stream, 'lunch', UserTopicVisibilityPolicy.unmuted);
         await tester.pump();
         check(tester.widgetList(find.text('lunch'))).length.equals(1);
       });
@@ -327,7 +329,7 @@ void main() {
           streams: [channel],
           subscriptions: [eg.subscription(channel)],
           unreadMessages: [message]);
-        await store.addUserTopic(channel, topic, UserTopicVisibilityPolicy.followed);
+        await store.setUserTopic(channel, topic, UserTopicVisibilityPolicy.followed);
         await tester.pump();
         check(hasIcon(tester,
           parent: findRowByLabel(tester, topic),
@@ -340,7 +342,7 @@ void main() {
           subscriptions: [eg.subscription(channel)],
           unreadMessages: [eg.streamMessage(stream: channel, topic: topic,
             flags: [MessageFlag.mentioned])]);
-        await store.addUserTopic(channel, topic, UserTopicVisibilityPolicy.followed);
+        await store.setUserTopic(channel, topic, UserTopicVisibilityPolicy.followed);
         await tester.pump();
         check(hasIcon(tester,
           parent: findRowByLabel(tester, topic),
@@ -356,12 +358,45 @@ void main() {
           streams: [channel],
           subscriptions: [eg.subscription(channel, isMuted: true)],
           unreadMessages: [message]);
-        await store.addUserTopic(channel, topic, UserTopicVisibilityPolicy.unmuted);
+        await store.setUserTopic(channel, topic, UserTopicVisibilityPolicy.unmuted);
         await tester.pump();
         check(hasIcon(tester,
           parent: findRowByLabel(tester, topic),
           icon: ZulipIcons.unmute)).isTrue();
       });
+
+      testWidgets('unmuted (topics treated case-insensitively)', (tester) async {
+        // Case-insensitivity of both topic-visibility and unreads data
+        // TODO(#1065) this belongs in test/model/ once the inbox page has
+        //   its own view-model
+
+        final message1 = eg.streamMessage(stream: channel, topic: 'aaa');
+        final message2 = eg.streamMessage(stream: channel, topic: 'AaA', flags: [MessageFlag.read]);
+        final message3 = eg.streamMessage(stream: channel, topic: 'aAa', flags: [MessageFlag.read]);
+        await setupPage(tester,
+          users: [eg.selfUser, eg.otherUser],
+          streams: [channel],
+          subscriptions: [eg.subscription(channel, isMuted: true)],
+          unreadMessages: [message1]);
+        await store.setUserTopic(channel, 'aaa', UserTopicVisibilityPolicy.unmuted);
+        await tester.pump();
+
+        check(find.descendant(
+          of: find.byWidget(findRowByLabel(tester, 'aaa')!),
+          matching: find.widgetWithText(UnreadCountBadge, '1'))).findsOne();
+
+        await store.handleEvent(eg.updateMessageFlagsRemoveEvent(MessageFlag.read, [message2]));
+        await tester.pump();
+        check(find.descendant(
+          of: find.byWidget(findRowByLabel(tester, 'aaa')!),
+          matching: find.widgetWithText(UnreadCountBadge, '2'))).findsOne();
+
+        await store.handleEvent(eg.updateMessageFlagsRemoveEvent(MessageFlag.read, [message3]));
+        await tester.pump();
+        check(find.descendant(
+          of: find.byWidget(findRowByLabel(tester, 'aaa')!),
+          matching: find.widgetWithText(UnreadCountBadge, '3'))).findsOne();
+      });
     });
 
     group('collapsing', () {
diff --git a/test/widgets/topic_list_test.dart b/test/widgets/topic_list_test.dart
index cf76ff3917..f87ddaf1ee 100644
--- a/test/widgets/topic_list_test.dart
+++ b/test/widgets/topic_list_test.dart
@@ -42,7 +42,7 @@ void main() {
     await store.addStream(channel);
     await store.addSubscription(eg.subscription(channel));
     for (final userTopic in userTopics) {
-      await store.addUserTopic(
+      await store.setUserTopic(
         channel, userTopic.topicName.apiName, userTopic.visibilityPolicy);
     }
     topics ??= [eg.getStreamTopicsEntry()];