Oh, so on the main site collection - where the full name has been set correctly - it changes back to the claims format as soon as you go to the my profile site? That is strange. Do you have the latest version of the FBA Pack (1.3.1)? You can check
the version from the FBA Site Configuration page. If there is no version on the site configuration page, you have a version < 1.3. Older versions of the FBA Pack had a bug where changes to lists in the site collection could trigger the full name being
If you have the latest version of the fba pack, cause the name to be reset by clicking on My Profile, and then check the SharePoint log files to see if any errors/exceptions occur that might give us a hint as to what's happening.