It was possible to return a marshalled command before previously added pending commands. And have the commands run out of order. For examples, an unsubscribe could be executed before all it's ack were run. This fix forces commands to allways be run in enqueued order.
incubator/activemq/trunk/activemq-core/src/main/java/org/apache/activemq/transport/stomp/StompWireFormat.java