Pivot Table dates grouped by Month & Year reverting to ungrouped date on refresh

I guess the Title says it all. The source data is stored in Access. I update the data in Access monthly. I have pivot tables that have dates and those dates are grouped by Month and Year. When I refresh the pivot tables the dates all revert back to un-grouped date. Any idea why this is happening? I had this same problem last month and I thought it was because I received the dates in my data with time (mm/dd/yyyy hh:mm:ss). But I made sure that all the dates are actual short format dates (mm/dd/yyyy) and I am still getting the issue.

Thanks

hey dflak. Thanks for the reply. I am taking a data file from Excel and importing it into Access. Then, the Pivot tables in my reports use the Access data. So are you saying to change the dates in my original source Excel data to integers (date serial number)? Where do you recommend that I convert those back into dates that look like dates. I am assuming that would take place in the Access table that is fed by the source data from Excel. But won't that cause me import errors if the source data is an integer and the receiving Access table field is formatted as short date ? What I need to do is group them into month and year in the pivot tables.

Thanks again

Sounds like an opportunity for me to learn something. When you say "...field being returned FROM Access." I read that as, when I pull the data from Access into Excel using my pivot tables. Are you saying that there is a way to go into a pivot table (or the data connection) in Excel and use worksheet functions like INT() on a particular field? Thanks for taking the time to explain.