bug#50660: 28.0.50; Text artifacting when the cursor moves over text under mouse face that originally displayed a box

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: larsi@gnus.org,  50660@debbugs.gnu.org
> Date: Tue, 21 Sep 2021 17:20:31 +0800
> 
> Yes, starting from emacs -Q, create a buffer in fundamental-mode, and
> evaluate:
> 
>   (insert (propertize "some sample text" 'face '(:box 10) 'mouse-face 
> 'highlight))
> 
> Highlight the text that was inserted, and move the cursor around inside
> the highlighted area.  The text will begin to jump all over the place.

Only the characters at the beginning and end of the box jump, so they
are the only ones that need an additional adjustment.  Right?