Open Radar

 
Summary:
Wiki calendars regularly loose configuration on Calendar.app clients

Steps to Reproduce:
Enable a group Calendar in wiki Server.
Configure a calendar Account on an OS X El Capitan Client with Calendar.app.

With a principal URL like this.
https://calendar.example.com:8443/principals/__uids__/wiki-foo/

Save and sync.

Expected Results:
This should just work and stay that way.

Actual Results:
After a random period of time, often only a few hours, sometimes it even works for a few days… the Calendar.app URL just automatically changes to the user's peronal calendar account which looks like this:

https://calendar.example.com:8443/principals/__uids__/E1AC7BB6-E8BC-4A65-84CA-1E311C698D87/

If the user has their own personal calendar account enabled as well, all appointments now appear doubled in their calendar.
They also cannot access the Wiki Group calendar anymore.


Changing the account back to a working group calendar requires the user to delete and reconfigure the whole account. Often even their personal account AND the wiki-group account. In many cases killing CalendarAgent via the Terminal is also required to make the changes get picked up by Calendar.app. Sometimes it is even necessary to fully reboot the Mac.

User's get highyl annoyed when this suddenly happens with many users of the account or when on the go/abroad and remote support is not easily available or simply impossible.



Regression:
This problem has persisted since at least OS X 10.6 (Snow Leopard) and has been filed as a bug repeatedly since then. Apple never bothered to fix it.


Notes:
This makes the Calendar Wiki-Group functionality pretty much useless, since it only works for a few hours or days without sysadmin interaction. This is an advertised feature of OS X Server.