bug#51550: 29.0.50; Customize Group INS buttons sometimes don't have a left box line

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Wed, 3 Nov 2021 00:03:00 -0700
> Cc: stephen.berman@gmx.net, 51550@debbugs.gnu.org
> 
> It seems like the entire line is shifted a pixel to the left when using
> :box, but only on the second consecutive line.  I tried experimenting
> with :box 1, :box -1, and I get the same result.
> 
> Are we sure that's not a bug in the display code?

I don't know, the arrangement of faces on that button is complicated,
to say the least.  I don't think I even understand which parts of the
display is the widget-field face applied to.  Can you show the
complete definition of the button face at the first line and the
non-first line?

> In any case, we could revert the commit for emacs-28 and continue 
> investigating
> on master.

Yes, I think we should do that.

Thanks.