Before attempting to enter the room, a MUC-compliant client SHOULD first discover its reserved room nickname (if any) by following the protocol defined in the Discovering Reserved Room Nickname section of this document.
+When a MUC service receives an <x/> tagged join stanza from an already-joined client (as identified by the client's full JID), the service should assume that the client lost its synchronization, and therefore it SHOULD send exactly the same stanzas to the client as if it actually just joined the MUC. The server MAY also send a presence update to the other participants according to the received join presence.