I just hit a nasty bug in Calendar.app and Reminders.app on Yosemite.
For some reason, calendars also appear in Reminders.app as empty reminder lists and reminder lists also appear in Calendar.app as empty Calendars. Even if I delete all of my calendars and reminder lists (I've got them all backed up), they get created back again.
I've noticed both calendars and reminders get stored under ~/Library/Calendars. I've been trying a lot of things to fix this up. As suggested in other articles I've tried deleting these files:
~/Library/Caches/com.apple.iCal(didn't exist)~/Library/Calendars/Calendar Cache*~/Library/Containers/com.apple.CalendarAgent/~/Library/Containers/com.apple.CalendarAgent.CalNCService/~/Library/Containers/com.apple.iCal/~/Library/Containers/com.apple.iCal.CalendarNC/~/Library/Preferences/com.apple.iCal.plist~/Library/Preferences/com.apple.iCalExternalSync.plist~/Library/Preferences/com.apple.iCal.helper.plist(didn't exist)
I've also tried deleting the whole ~/Library/Calendars directory and I've restarted my mac many times during this whole process.
Yet every time I go back to Calendar.app or Reminders.app, the buggy calendars and reminder lists keep creeping back again.
I don't know what to do anymore now… any suggestions would be welcome!
Edit: I seem to have reached a state of sanity out of this mess… at last!
Searching up the ~/Library/ directory, I found what appears to be the culprit causing me this problem. There is a file that's being generated by some sync services from Apple located at ~/Library/Application\ Support/SyncServices/Local/TFSM/com.apple.Calendars/data.syncdb. I'm not sure what process is updating this, but I'm using iTunes to sync local calendars to my iPhone and I suspect it probably has something to do with this. So perhaps the bug is not in Calendar/Reminders but really in iTunes or the SyncServices.
So I've deleted that file as well as all files under ~/Library/Containers/com.apple.CalendarAgent/Data/Library/Calendars/ and restarted OS X. When I opened Calendar.app, the calendars one should get by default on a new user account were there: Home and Work, and in my case Birthdays and Holidays too. Reminders.app also showed an empty Reminders list, which is fine too. So then I proceeded to restore my calendars and reminders from my backups.
Synchronization in iTunes is now OK, but the reminder lists still shows up as calendars for some reason (seems like a bug here too). If I manually select calendars from Calendar.app, everything seems to work just fine.
My last resort would have been to move all my stuff to a new user account (assuming the problem was due to a buggy state with my current user account – as suggested by bmike), but luckily I don't have to do that tedious task, at least for now.
Using OS X 10.10.5 and iTunes 12.2.2.25.
Best Answer
I would say, you're off the wrong foot deleting files in ~/Library since the storage there changes from version to version (and sometimes even build to build).
If I have AppleCare - I just call them and they have internal documents and the ability to get you the exact steps for your exact situation.
If I don't want to call Apple or I have time to work on the issue - Here's the strategy I've employed to clean things out when iCloud is messed up. It takes me far less time to do it this way. :-)
If there were issues syncing one bucket - contact Apple Support or install a new OS and re-test on the new OS.
If there are no issues - then turn on all of the buckets in the new account to verify things are OK.
At that point, you know these things:
At that point, you can make a decision to migrate the user from the broken user (it might be broken from you deleting things or a bug or just bad luck - but it's clearly broken).
If you really want to clear things out, it would be best to just ask separately. The steps to clear Calendar are not the same as clearing Reminders.
Also keep in mind - other devices can inject data into the cloud - you might have to isolate the problematic Mac and the Cloud data in some cases.