joomla 1.5.23, cb 1.4, gj 2.3:
Perhaps I don't understand, but it seems to me a bug:
I have a user in my group. He is not owner of the group. But in his profile, this group is in the tab "my groups" and also in the tab "joined groups".
I think, in the tab "My groups" of this user, the group should not be visible!