[Bug][Calendar]: Placeholders are only removed from the inviter

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

When using the new "meeting proposal" feature placeholder appointments are created in everyones calendar. When selecting the final decision, placeholders are removed from the inviter, but not from the invited people.

Steps to reproduce

1. Create an meeting proposal workflow
2. Invite collegues
3. Select one of the suggested appointments, after everyone voted for their preferred appointment

Expected behavior

When using the new "meeting proposal" feature placeholder appointments are created in everyones calendar. When selecting the final decision, placeholders are removed from the inviter and the invited people.

Nextcloud Server version

36

Operating system

No response

PHP engine version

No response

Web server

No response

Database engine version

No response

Is this bug present after an update or on a fresh install?

No response

Are you using the Nextcloud Server Encryption module?

No response

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

No response

Reproduce the meeting proposal workflow in the Nextcloud Calendar app, then trace how placeholder appointments are removed after a final appointment is selected. Compare the inviter and invited users' calendars; done means placeholders are removed for everyone involved, with regression coverage for the reported workflow.