bug#48740: 28.0.50; Composition text property is not always honoured

[Eli Zaretskii]

> From: Ihor Radchenko <yantar92@gmail.com>
> Date: Sun, 30 May 2021 15:35:51 +0800
> 
> I encountered a very strange issue with text composition using
> prettify-symbols-mode. It happens with text copied from an Org buffer to
> Org agenda buffer when the composed text has >4 chars length.

That probably means the composition property is somehow invalid or
something.

> Recipe:
> 1. git clone https://github.com/yantar92/org
> 2. cd /path/to/org
> 3. git checkout feature/org-agenda-fontify
> 4. make clean
> 5. make
> 6. emacs -Q -L ./lisp/ -l org -l /tmp/1.el ~/Org/inbox.org
> 5. M-x org-agenda < t
> 6. M-x org-todo on the first item selecting "ONGOING" state
> 7. Note that "ONGOING" keyword gets replaced with composed icon (as
>    defined in 1.el). M-x describe-text-properties shows composition set
>    to (0 7 [128119])
> 8. M-x org-agenda-redo-all
> 9. The "ONGOING" keyword is not replaced by composed icon anymore. Yet,
>    M-x describe-text-properties still shows composition set to (0 7
>    [128119])

Step 3 above fails here:

  $ git checkout feature/org-agenda-fontify
  error: pathspec 'feature/org-agenda-fontify' did not match any file(s) known 
to git.

Anyway, would it be possible to prepare a recipe that is simpler, and
doesn't involve checking out and building a large package?  That'd
make debugging this much less unpleasant.  TIA.

Alternatively, show the text in the problematic buffer with all the
text properties, overlays, and other stuff around the problematic
place, and maybe that alone will suffice (but in that case it would
probably also be easy to generate a simpler text case...)