Analytic Snapshot based on Summary report grouped by Date field

[huskerwendy]

I'm trying to create an analytic snapshot using a summary report where the first grouping is the Purchase date grouped by calendar month year. The snapshot will be executed on the first day of the month for the data from the previous month. I want to map the Purchase Date to a Month/Year field in the snapshot so that the Month Year field has "November 2012" or I could have two fields Month and Year or even the last day of the month for every record. The problem is no matter if I create the field as a text field or a date field, when the snapshot runs it populates the field with different dates from November. I'm assuming that it's just picking the last date for each grouping. Is there a way to do this?

[huskerwendy]

The above image is the field mappings and below is the report that populates the snapshot.