odbc returns non-static data to Access?

I have an Access database that links to two Visual FoxPro tables. Queries compare an Access table to the VFP tables to determine which rows in Access aren't in the VFP tables.

Results for the same query vary by a couple each time I run the query - everything is local, nothing "Visual FoxPro" is running, so the tables are essentially closed files.

I imported the VFP tables to Access, and now I get good clean static data, with the same row count every time.

What the heck is going on with this?