Issue sorting date field on underlying data

Issue sorting date field on underlying data

Hi,
 
My MM-dd-yyyy date fields do not sort properly for Underlying Data tables in a report. On the main table, there is no problem with the sort.  I have formatted the field to use MM-dd-yyyy date format.
 
Here's a screenshot of what I see when I sort by date on Underlying Data fields.  Everything is sorted by day of month, so I see all entries from the 31st of each month, then the 30th, then the 29th, etc.