What has Mountain Lion done to iCal sync?

I'm seeing lots of questions about iCal post-Mountain Lionon these forums, but far fewer answers on this one!

I have four calendars on my iPhone 4 that run my life. Pre-Mountain Lion upgrade on my iMac they all synched perfectly well via iCloud with my iPad and iMac.

Since upgrading to Mountain Lion, the iPhone and iPad still sync properly. However, when I went into iCal on the iMac two days back, for the first time since the Mountain Lion upgrade, I think, none of my calendars were there. The only calendar showing was one for birthdays, which I don't ever recall setting up. My iCloud account was missing from iCal's "Preferences". Adding it back in restored all of my calendars, and I thought I'd sorted this problem.

However, today, I opened iCal on the iMac again today, and my calendars were all missing again. Just that "Birthdays" calendar there.The iMac hasn't been powered down or re-started during the time since I reinstated the iCloud details to iCal.

So, today, I've added my iCloud account to iCal's preferences again, but I don't have much faith that this alone is the solution, given that I did that two days ago too.

Anyone else getting this? Seems a basic sync error, but I can't work out why iCal should be "forgetting" iCloud accounts that have been added?

Tom