Is it a bug. when hit the "enter" key , got a step with two paragraph

[4-1-1]

Hit "enter" at an empty line to create a new paragraph.
But the tr step will carry two paragraph

[Saul-Mirone]

That's by design of prosemirror.
https://codesandbox.io/s/heuristic-rhodes-fqxloy?file=/src/index.ts

[4-1-1]

It's quite wired.
I need to calc the content length change by the step. to get the total length and avoid the serializing.

A lot of "sigh"!