bug#26742: Display bug with composed strings

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 26742@debbugs.gnu.org
> From: Clément Pit--Claudel <clement.pitclaudel@live.com>
> Date: Tue, 2 May 2017 11:40:08 -0400
> 
> On 2017-05-02 04:15, Eli Zaretskii wrote:
> > If you change the font use for displaying ℝ and ≤, does the problem go
> > away?
> 
> No: it seems to happen both in my heavily-customized Emacs and in emacs -Q.

That doesn't necessarily answer my question, unless the font used to
display those two characters is different in "emacs -Q" and in your
customized session.

If both use the same font, please try forcing Emacs to use some other
font, perhaps one that is more wide-spread on GNU/Linux systems, and
see if that changes anything.

If that doesn't help, then the next question is: is this problem
specific to these two characters, or is it more general?  If the
latter, I suspect the shaping engine used in your case is the culprit,
so perhaps upgrade your libotf, libm17n-flt, and m17n-db packages.  If
you already have the latest versions of these, it would be time to ask
Handa-san to chime in and look into this.