On Sun, May 31, 2020 at 6:01 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > Date: Sun, 31 May 2020 20:50:07 +0300
> > From: Eli Zaretskii <eliz@gnu.org>
> > Cc: 41454@debbugs.gnu.org
> >
> > The problem is that the entire sequence of characters that matches
> > the regexp is passed to the shaper, and the result is stored as a
> > single composition.  And we have special code in the display engine
> > not to break sequences of potentially-composed characters when
> > handling faces (see compute_stop_pos).  So I think there might be
> > some bug there which shows when a composition comprises more than a
> > single grapheme cluster, and some face is applied to them.
>
> On second thought, I'm not sure this is the right place to look at.
> It could be fill_gstring_glyph_string and BUILD_GSTRING_GLYPH_STRING
> instead (and the respective *term.c display functions).

Thanks for the hint! You were absolutely correct.