bug#50798: 28.0.50; Tab line close button is off-center until it is highlighted with the mouse

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: larsi@gnus.org,  luangruo@yahoo.com,  50798@debbugs.gnu.org
> Date: Sun, 03 Oct 2021 20:42:56 +0300
> 
> It solves the problem because tab-line-close-highlight doesn't inherit
> from other faces.  It's face inheritance that caused the problem
> with vertical movement of the button.

I'd still like to understand why this happens.  It sounds like a bug.

You said you found some coordinates miscalculated, but didn't provide
any details.  Could you please provide those details, so I could try
to look at that?  Debugging this is notoriously hard, because the code
is entered upon almost every mouse movement, so it is important for me
to know which code I'm investigating to be able to set up the
breakpoint conditions that avoid triggering at non-interesting
moments.