Rooms is allowing owners, admins and outcasts to be duplicated
MUCRoomImpl#addOwner(String bareJID, MUCRole sendRole)
MUCRoomImpl#addAdmin(String bareJID, MUCRole sendRole)
MUCRoomImpl#addOutcast(String bareJID, String reason, MUCRole senderRole)
are not checking if the user has already the specified affiliation. Therefore, the same JID may end up in the list duplicated. There are not known consequences for this issue.