The UserInterface "search for usage" on a user object only lists a reference within a notification object. What the result list does not show is the fact that this user is also member of 2 usergroups objects.
This is a behaviour by design, and there will be no change for the moment.
It is a technical reason. The connection between USR and USRG is not done by the name but by OH_IDNR. Thats the reason why you can change the name of the User but he still stays in the Group.