Right arrow navigation not working in some cases

[Störm]

Moved from: humhub/humhub#4950

Steps to reproduce

Create a post
Write a phrase in bold
Press 'Enter' for a new line (not Shift+Enter)
Write a further phrase in regular text
Attempt to navigate with the cursor using arrow keys - from the end of the line in bold to the beginning of the line in regular text

Expected:

The right arrow key will move from the end of the emboldened text line to the beginning of the regular text line

Currently:

The right arrow key does not do anything. (The cursor will move left or down with other arrow keys, but not right with the right arrow key.)

Tested

Two installations of Humhub and Humhub community: issue occurs

https://prosemirror.net/ : issue does not occur
https://ckeditor.com/ckeditor-5/demo/ : issue does not occur