Google appears to have something against people with December birthdays, omitting the month from the feature which allows users to add birthdays and anniversaries to their contacts list.
It's only Android 4.2's People app that contains the bug, with the Calendar app working normally, and affects users of Nexus 4 and 10 devices, as well as some Nexus 7s.
It was first spotted on November 14 by a user who asked for help on the company's support forum.
"Today I was inserting birthday of a friend in my contact list so that I can sync the birthdays in my calendar," he wrote.
"I noticed that the December month is missing. When I pressed new event the calendar came but it was not having the option for the month December."
The problem appears to have been caused during a fix of an earlier bug, and relates to the way the months are numbered. It seems that the array dealing with the months is zero-indexed, in other words running from 0 to 11 - but that the month numbers themselves run from 1 to 12.
It's not the only problem that's been reported with the new OS, with users complaining of random reboots, Wifi problems and disappearing apps.
The problem's been acknowledged by Google, which one presumes will attempt to get a fix out in time for Christmas. Let's just hope Santa isn't using 4.2 himself.