Chobby tries to rejoin MM after loading even if the player just got invited into a MM match, or if he started to play in another match. Chobby should only rejoin MM if the player started spectating a game or playing singleplayer.
This has been going on for longer so the server now prevents users from rejoining MM in these cases, but it's ugly for users to be shown a "You can't rejoin MM" message, when they wouldn't want to anyway.