bug#18793: 24.4; zero width rectangular selection displaces text

[Eli Zaretskii]

> Cc: 18793@debbugs.gnu.org
> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Thu, 05 May 2022 15:16:40 +0200
> 
> Carlos Pita <carlosjosepita@gmail.com> writes:
> 
> > 1) Put the point at the beginning of the following sequence of a's.
> > 2) Start a rectangular selection with C-x Space.
> > 3) Move the point one char to the right.
> > 4) Move it one char to the left so that it returns to the left margin.
> > 5) Repeat 3 and 4 a number of times.
> >
> > aaaaaaaaaaa
> >
> > Do you see how the sequences of a's moves back and forward? 
> 
> I can confirm that this behaviour is still present in Emacs 29.

AFAIU, that's a feature: we are trying to indicate the existence of
the selection, even though its width is zero.  Type "M-x
describe-text-properties RET" at the first character.  The indication
must take up some space on display, so it moves the following text to
the right.