I’ve got the same problem, but I’ve realised that it’s because I have it set to dd/mm/yy – if I set it to the default of mm/dd/yy, it’s fine. Also, if I have it set to dd/mm/yy, and select a date that would work for mm/dd/yy, (eg 06/05/13) that also validates.
Unfortunately mm/dd/yy isn’t going to work for my client who isn’t the sharpest tool in the shed. ??