As stated in XEP-0124, http://www.xmpp.org/extensions/xep-0124.html#rids-order :
"When a client makes simultaneous requests, the connection manager may receive them out of order. The connection manager MUST forward the stanzas to the server and respond to the client requests in the order specified by the 'rid' attributes. The client MUST process responses received from the connection manager in the order the requests were made."
When Openfire recevies two BOSH requests out of order, i.e. the one with the greader rid arrives first, it responds to the latter with:
<body xmlns="http://jabber.org/protocol/httpbind" type="terminal" condition="item-not-found"></body>
Subsequent requests from the client will be responded with 404-Not Found, since the session is dropped.