Task related to itself is not displayed (but counted) and can break client apps

Steps to reproduce

The following task (while clearly incorrect) is not displayed/listed even though the counts next to task lists do include it:

BEGIN:VTODO
CREATED:20220927T091609Z
LAST-MODIFIED:20250111T154229Z
DTSTAMP:20250111T154229Z
UID:88170931360831689
SUMMARY:Problematic task (task is NOT displaying)
PRIORITY:1
STATUS:NEEDS-ACTION
RELATED-TO:88170931360831689
X-MOZ-LASTACK:20250111T154229Z
DUE;TZID=Europe/London:20240930T000001
SEQUENCE:1
X-MOZ-GENERATION:2
PERCENT-COMPLETE:0
BEGIN:VALARM
ACTION:DISPLAY
TRIGGER;RELATED=END:PT0S
DESCRIPTION:Default Tasks.org description
END:VALARM
END:VTODO

I also attach a minimal(-ish) example of a full task list which has the broken task as well as one set of main task plus 4 substasks (as one of these sub tasks was the one with the same name as the broken task though I am sure that was just incidental): tasklist-2025-02-28 (example).ics.txt

Expected behavior

The task should be displayed, and I guess the server should tidy up/remove the incorrect RELATED-TO tag as this can break client apps as well (see Tasks.org app, issue #3367.

Actual behavior

The task (while clearly incorrect) is not displayed/listed even though the counts next to task lists do include it. (For the Tasks.org app it breaks the display of any tasks in relevant filters. I suspect the author will tweak the app to make it more robust, but the server sanitising incorrectly formatted tasks is probably an appropriate action.)

Calendar app version

5.1.2

CalDAV-clients used

Thunderbird Lightning, DAVx5, Tasks.org app

Browser

Firefox 135.0.1

Client operating system

Linux Mint 22.1

Server operating system

Debian 11 (bullseye)

Web server

Nginx

Database engine version

MariaDB

PHP engine version

PHP 8.2

Nextcloud version

31.0.0

Updated from an older installed version or fresh install

Updated from an older version

List of activated apps

Will provide if deemed relevant

Nextcloud configuration

Will provide if deemed relevant

Web server error log

Will provide if deemed relevant

Log file

Will provide if deemed relevant

Browser log

Will provide if deemed relevant

Additional info

Issue was identified via a bug submitted to Tasks.org app, issue #3367.

Use the attached tasklist-2025-02-28.example.ics.txt and the self-referential VTODO as the reproduction fixture; first import it into Calendar 5.1.2 and compare task-list counts with displayed tasks. Check the related Tasks.org issue for the client failure. Done means the task is displayed consistently with the counts and the invalid RELATED-TO data no longer breaks affected clients.