bug#39390: 28.0.50; prettify-symbols-mode confuses display when start/end faces are different

[Eli Zaretskii]

> Cc: 39390@debbugs.gnu.org
> From: Raphael 'kena' Poss <knz@thaumogen.net>
> Date: Sun, 16 Feb 2020 21:47:43 -0500
> 
> On 16-02-2020 15:23, Eli Zaretskii wrote:
> 
> > Please do, and thanks.
> 
> My pleasure:
> 
> https://asciinema.org/a/3nOh1zCJYHOeQ4uXk0rQ9akv8

Ah, "emacs -Q -nw"!  You never said that before, and your recipe
explicitly says "emacs -Q".

With -nw, I do see two @@ as you say, and also some irregularities in
the display.  But your data is not according to documentation, so I
guess that's why the result misbehaves.