I started to suspect the issue was with MeeBirthdays as soon as I started looking at this more closely. The events that MeeBirthdays creates are really very strange. Here is an example for a birthday that is supposed to be on 7 Feb every year. Now when I look in the Calendar for that day the next day it comes up, 7 Feb 2012, I see the person's name, let's say Mary Smith, with her age on that day in 2012, and the event is marked as All Day. So far so good.

If I now click on that event to see more details about it I already see something that is strange. The Starts date has changed to 21 Dec 2012 at 00:00, the Ends date is 1 Jan 4712 at 01:00. Both dates are now shown incorrectly, and the end date should even be possible.

I did try and edit it, against your advice, and I just see the event has become today's event in the Feed but is nowhere to be seen in my actual Calendar.

MeeBirthdays seems flawed anyways because it shows the person's age as the same every year. I'm going to have to delete that Calendar (luckily I was just setting things up and there is no other events in that one) and uninstall MeeBirthdays and not use it.

The problem is partly the fault of Nokia for not (a) providing an anniversary event type that is found in the N900, and (b) not integrating the Contact's birthdays in the Calendar already - probably (a) and (b) are connected.