Complete report in the forum thread. Openfire doesn't obey:
If the user requesting registration requirements is not allowed to register with the room (e.g., because that privilege has been restricted), the room MUST return a <not-allowed/> error to the user. If the user is already registered, the room MUST reply with an IQ stanza of type "result" that contains an empty <register/> element as described in XEP-0077. If the room does not exist, the service MUST return an <item-not-found/> error.