Google has officially recognised the Android 4.2 December birthday bug and has announced that it will be bringing a fix very soon.
The glitch, which was identified recently, resulted in the missing December month in the date selector of the People (contacts) app in Android 4.2.
The bug fix is expected to be released as an OTA update.
Here is the full statement from Google on the official Android Google+ page:
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.