Minor Description
Due to the adding of the new properties to TimeStampingBrokerPlugin the "message.setTimestamp()" was misplaced and is set to early in the code.
The line need to be placed as the last line in the method send() as was in 5.2.
In addition the Plugin doesn't handle the scenario where the Broker is running "behind" its client. What is happening is that it's setting the Expiration and TimeStamp to historical values in the client perspective causing them to be discarded by the clients.
I have supplied a patch that solves both issues.