Deletion of a single occurence in a series sends mail to attendees that is an invitation

[Ganneff]

Steps to reproduce

1. Create an event that repeats, once a week, with some attendees. They get a proper invitation mail, all fine.
2. Cancel/Delete a single occurence "later" on
3. Mail is send to attendees - and it closely mirrors the initial invitation mail. It says "Invite", has an "Accept" and "Decline" Button, and all the event details.

Expected behavior

Mail gets send to attendees, saying "Event cancelled" (or something more specific for just that occurrence).

Actual behaviour

Wrong mail, full invitation, send.

Calendar app version

3.4.2

CalDAV-clients used

None

Browser

Firefox

Client operating system

Doesn't matter

Server operating system

Debian Bullseye

Web server

Nginx

Database engine version

PostgreSQL

PHP engine version

PHP 8.0

Nextcloud version

24.0.3

Updated from an older installed version or fresh install

Updated from an older version

List of activated apps

No response

Nextcloud configuration

No response

Web server error log

No response

Log file

No response

Browser log

No response

Additional info

No response

[Ganneff]

It appears that the attached ics file contains "EXDATE" lines with the cancelled dates. Which is fine, but not much helpful, as that's the last thing people look at, if the mail itself is just wrong.

[ChristophWurst]

Likely related to https://github.com/nextcloud/calendar/issues/3919.