required not working?

I updated from a patched drupal 5 version to the 6 beta, and had a few hickups... deleting the entry in the system table and reinstalling has fixed most, but even though I indicate roll selection is mandatory on sign up, it is not mandatory on the form. I suspect this is merely a bug due to my previous patched version. Perhaps someone could advise how to do a complete uninstall of previous versions? (if this is genuinely not a bug)?