diff --git a/src/js/core/tools/Helpers.js b/src/js/core/tools/Helpers.js
index 078e17508..4684d34ff 100644
--- a/src/js/core/tools/Helpers.js
+++ b/src/js/core/tools/Helpers.js
@@ -32,7 +32,7 @@ export default class Helpers{
 		return output;
 	}
 
-	static deepClone(obj, clone, list = []){
+	static deepClone(obj, clone, circularRefs = new WeakMap()){
 		var objectProto = {}.__proto__,
 		arrayProto = [].__proto__;
 
@@ -40,23 +40,22 @@ export default class Helpers{
 			clone = Object.assign(Array.isArray(obj) ? [] : {}, obj);
 		}
 
+		//map each source object to its clone so shared/circular references resolve
+		//to the same clone instead of being re-cloned (O(1) lookup vs a scanned list)
+		circularRefs.set(obj, clone);
+
 		for(var i in obj) {
-			let subject = obj[i],
-			match, copy;
+			let subject = obj[i];
 
 			if(subject != null && typeof subject === "object" && (subject.__proto__ === objectProto || subject.__proto__ === arrayProto)){
-				match = list.findIndex((item) => {
-					return item.subject === subject;
-				});
+				const existing = circularRefs.get(subject);
 
-				if(match > -1){
-					clone[i] = list[match].copy;
+				if(existing){
+					clone[i] = existing;
 				}else{
-					copy = Object.assign(Array.isArray(subject) ? [] : {}, subject);
-
-					list.unshift({subject, copy});
+					let copy = Object.assign(Array.isArray(subject) ? [] : {}, subject);
 
-					clone[i] = this.deepClone(subject, copy, list);
+					clone[i] = this.deepClone(subject, copy, circularRefs);
 				}
 			}
 		}
diff --git a/test/unit/core/tools/Helpers.spec.js b/test/unit/core/tools/Helpers.spec.js
new file mode 100644
index 000000000..a4786a67d
--- /dev/null
+++ b/test/unit/core/tools/Helpers.spec.js
@@ -0,0 +1,73 @@
+import Helpers from "../../../../src/js/core/tools/Helpers";
+
+// deepClone must produce an independent deep copy while preserving shared and
+// circular reference identity (the case the WeakMap keying must get right).
+
+describe("Helpers.deepClone", () => {
+	test("deep copies nested objects and arrays (values equal, refs distinct)", () => {
+		const src = { a: 1, nested: { b: 2, list: [1, 2, { c: 3 }] } };
+		const out = Helpers.deepClone(src);
+		expect(out).toEqual(src);
+		expect(out).not.toBe(src);
+		expect(out.nested).not.toBe(src.nested);
+		expect(out.nested.list).not.toBe(src.nested.list);
+		expect(out.nested.list[2]).not.toBe(src.nested.list[2]);
+	});
+
+	test("mutating the clone does not affect the source", () => {
+		const src = { nested: { n: 1 }, arr: [{ x: 1 }] };
+		const out = Helpers.deepClone(src);
+		out.nested.n = 99;
+		out.arr[0].x = 99;
+		expect(src.nested.n).toBe(1);
+		expect(src.arr[0].x).toBe(1);
+	});
+
+	test("preserves shared references (same object referenced twice -> one clone)", () => {
+		const shared = { v: 1 };
+		const src = { a: shared, b: shared };
+		const out = Helpers.deepClone(src);
+		expect(out.a).toBe(out.b); // same clone instance
+		expect(out.a).not.toBe(shared); // but a copy, not the original
+	});
+
+	test("handles a nested circular reference (identity preserved, no infinite loop)", () => {
+		const a = { name: "a" };
+		const b = { name: "b" };
+		a.child = b;
+		b.parent = a; // circular
+		const out = Helpers.deepClone(a);
+		expect(out.name).toBe("a");
+		expect(out.child.name).toBe("b");
+		expect(out.child.parent).toBe(out); // circular ref points back to the clone of a
+		expect(out.child.parent).not.toBe(a);
+	});
+
+	test("handles a self (root) circular reference", () => {
+		const obj = { name: "root" };
+		obj.self = obj;
+		const out = Helpers.deepClone(obj);
+		expect(out.name).toBe("root");
+		expect(out.self).toBe(out);
+	});
+
+	test("handles many circular refs without blowing the stack or corrupting identity", () => {
+		const root = {};
+		let prev = root;
+		for (let i = 0; i < 500; i++) {
+			const node = { i, back: prev };
+			prev.next = node;
+			prev = node;
+		}
+		const out = Helpers.deepClone(root);
+		// walk and confirm each node's back-ref resolves to the correct cloned node
+		let cur = out;
+		let count = 0;
+		while (cur.next) {
+			expect(cur.next.back).toBe(cur);
+			cur = cur.next;
+			count++;
+		}
+		expect(count).toBe(500);
+	});
+});