bug#50424: 27.2; Tab bar button mouse face not clearing entirely

[Eli Zaretskii]

> Date: Mon, 06 Sep 2021 16:12:56 +0800
> From:  Po Lu via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> 
> Enable tab-bar-mode, move the mouse pointer over the "+" button used to
> create new tabs.  Once the button is highlighted by displaying a relief,
> move the pointer back outside the tab bar.
> 
> While most the relief around part of the button will be cleared, part of
> the left side of the relief that surrounded the "+" button when it was
> highlighted will be retained.
> 
> To the best of my knowledge, this also appears on Emacs 28.

FWIW, I cannot reproduce this, neither in Emacs 27.2 nor in Emacs 28.

Maybe this is window-system dependent?

Alternatively, if you have some "optimization" features enabled in
your video drivers, disable them and try again.