If you recently purchased a new Nexus device, you will be happy to know that Google has released a software update for the Google Nexus 4, Google Nexus 7 and Google Nexus 10. Your device will be updated to Android 4.2.1 with this 1.1MB update which is currently rolling out to supported devices. The purpose of this update is to fix the December bug on the Contacts app.
The bug which users noticed on Android 4.2 devices didn't allow any events to be set between November and January as it was missing the month of December. However now that the update has arrived (thankfully before December) you can add December events.
source – XDA Developers | Talk Android