time: unexpected behavior for time.AddDate()

[toxeus]

It seems like time.AddDate() is not correctly handling the number of days per month. This sometimes leads to unexpected behavior for time.AddDate() that can be best illustrated with a short code snippet:
http://play.golang.org/p/BS3tHHRxoA

[ianlancetaylor]

This is working as documented. There is no September 31 or November 31, so the date is normalized.