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

[Ihor Radchenko]

Hello,

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.

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])

The 1.el and inbox.org are attached.

Best,
Ihor

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, cairo version 1.16.0)
 of 2021-05-29 built on localhost
Repository revision: 2003a407c8bdf79dabe4f782039706d91c4fd9c5
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Gentoo/Linux

inbox.org
Description: Lotus Organizer

1.el
Description: application/emacs-lisp