Bug in undo/redo with additional new lines

That little bug exists on Windows and Linux. In version 2.0.0 and 1.2.0.

First open a file with color emojis

Then writing fast and wild some "text".

Then Undo with Ctrl+Z or over the menu

And then redo with Ctrl+Y or over the menu

After the redo you have one or more new lines.
Possible with one single letter, which was before part of the longer "word"

Reproduce the sequence on Windows or Linux: open a file containing color emojis, type quickly, then use Ctrl+Z and Ctrl+Y or the corresponding menu actions. Trace the undo/redo entry points and verify that redo restores the text without introducing additional new lines, including when the edited text is a single letter from a longer word.

Written by the indexing model from the issue text.