Time Intelligence Week calculation is incorrect

I'm having an issue with using the time intelligence week attribute when creating a filter in performance point.  The Year, Quarter, Month, etc all work correctly except week.  For instance, if I use (week-1) on 11/26/2013 it should translate to the 47th week but instead it is translating to the 40th week.  However if I use WeekToDate that translates correctly.  Any ideas why week is not translating to the correct week of the year?

Thanks.