As per: XEP-0045: Multi-User Chat 10.1.1: “Note: If the presence stanza sent to a nonexistent room does not include an element qualified by the ‘http://jabber.org/protocol/muc’ namespace as shown above, the service SHOULD create a default room without delay (i.e., it MUST assume that the client supports groupchat 1.0 rather than MUC and therefore it MUST NOT lock the room while waiting for the room creator to either accept an instant room or configure a reserved room).”
Openfire keeps the room locked until either a instant room request or reserved room request is sent.