One of the things I remember from my old programming daze is that trying to sync data across multiple devices is really, really hard. Even after you test and test, something comes up and messes up the data.
Our latest syncing problem has to do with our internet calendar and phone. Some of the birthdays are now set at December 31st, 1904 (?), but not all of them. And only on the phone. Weird. Somewhere in the back of my brain I seem to recall a dusty old memory about this being related to memory or switching from 32 bit to 64 bit and OMG I almost fell asleep there by boring myself!
Anyhoo, reboot, start over and hope for the best – this is not really a big problem. (First world problems…)