Unable to remove usergroups from a profile

Hi Alex
I checked the FAQ before, and I could not find any comments to my issue.
When I add a user, and connect him with a user group everything works fine. But after saving the profile, I am not able to change the usergroup any more. So If I want to exclude the profile from one usergroup later, it is impossible, even with admin rights. I can still add a user group but not remove.
I also deactivated all other plugins, to find any collisions with other plugins, but nothing changed.
Is this standard or do I just miss to check an option?

Thanks a lot for a soon reply.

Best regards
Michael