I tried to put a thousand of users into one MUC room. Server was working very slow but it did. When I disconnected all clients server normally removed them from MUC room and closed sessions, but some presences (about 50) wasn’'t recieved. May be there is problem with network, may be with client programs (Psi, JAJC) I used to look at MUC room occupants. But it looks like concurrency error when sending groupchat presence.