The Android 4.2 (still Jelly Bean) was released for the (ASUS-made) Nexus 7 slate back-to-back with the new LG Nexus 4 smartphone and Samsung Nexus 10 tablet two weeks ago. Soon after the users noticed December was missing from the Contacts app.
Well, the Google developers have finally squashed this bug (among others) with the Android 4.2.1 release. Available for all three devices, the update is already seeding globally.
The new 4.2.1 OTA update weighs just 1.1MB and makes December reappear in the Contacts app and fixes the Bluetooth issues lots of users were experiencing.
If you didn’t get the notification yet, you should just go and check for updates manually – it should be there waiting for you.