This is a new one on me. The date widget we've been using (I don't have the exact library handy to blame), actually repeats a day the first weekend of November. So this year for instance, Sunday and Monday both show up as Nov 2. Every year it's always November, and it's always the first weekend. We just found it so we haven't yet determined the cause, but guesses range from daylight savings time to leap year to rounding issues.
I like the theory that it's politically motivated, to make people think that November 4th (voting day!) is actually Wednesday.