OK, I guess it is not an issue anymore.

I changed to the DateBox and that does not do this. On the DateTimePicker this 00 month would appear only when the actual date was either null or 1/1/1800. Then when a date was entered it would change the month to 00 when you tabbed out of the column.

I've tried different things over here but wasn't able to reproduce it. Can you post a simple sample which would?

When the user enters 12/31/2012 or any date manually without using the calendar, when you tab out of the date column the month becomes 00. Do you know what may be going on?