Best practice approach is to only use one table source per form to avoid potential issues like this one.
While I agree that using multiple tables in a form's recordsource query requires a greater understanding of relationships and joins, I don't agree that restricting forms to single-table recordsources is a "best practice". It's just a more
advanced practice.
Dirk Goldgar, MS Access MVP
Access tips: www.datagnostics.com/tips.html