changing subj in GC when not allowed should fall back to previously set and not to the illegal [see insinde]
in a room you cannot always change the subj in fact you change it you press ENTER (or Set) and you may get a chat room that will inform you about the error
a) It's ok for now to give such errors in chats. In the future I would preferer to give them as Error Dialogs though
b) After we get the error the user has to refresh (if he has tabs or else he cannot do anything) to get the previous valid subj. If he doesn't do that, he has the error saying he cannot set subj, but he sees his subj in the room [of course the server won't print /me switched the subject to: NEW_SUBJ]
but the user might not notice that.
solution:
catch this error and show it in an Error Dialog and also undo the change in the subj (on creation of a room store the subj so you can revert to it)