The issue of Google forgetting to include the month of December in the People app in Android 4.2 has been very well publicized. Basically, there is no way to enter a date in December when in the People app, meaning you couldn’t add any dates (birthdays, anniversaries) to contacts if they happen to land on December. It’s funny, how big an oversight this is.
Google finally acknowledged the issue on the Android Google+ account, and they had this to say:
We discovered a bug in the Android 4.2 update, which makes it impossible to enter December events in optional fields of the People app (this bug did not affect Calendar). Rest assured, this will be fixed soon so that those of you with December birthdays and anniversaries won’t be forgotten by your friends and family.
Hopefully this bug will be addressed soon. For socialites (or anyone with friends, really), this may be a pretty major issue. If it’s affecting you, you could always go to the Google Contacts website and edit birthdays and other dates from there. But for now we wait for Android 4.2.1, maybe there will be a few more goodies in store.