In this testcase, as you didn't specify acknowledgementInterval in wsdl ws-rm policy configuration, so will use default value 0 for acknowledgementInterval, which means both client and server side will use ImmediateAcknowledgement, trying best effort to not create out-of-bind SequenceAcknowledgement, this can gain higher performance.
The expected behavior in this case is that
For server side, the behavior is put SequenceAcknowledgement header to the response message, for client side, the behavior is put SequenceAcknowledgement header to next invocation request message in the rm sequence.
So what you see here "combine the WS-RM sequence acknowledgement and response from the service into the same message and send it to the client's decoupled endpoint" is expected behavior for server side, it leverage the response message to piggyback the SequenceAcknowledgement, which avoid creating another out-of-bind SequenceAcknowledgement, so get higher performance.
The problem is actually from the client side when receive last response message which has SequenceAcknowledgement header, client will never ack the last response because there's no next invocation request which can piggyback the SequenceAcknowledgement header, and so server side will always resend the message.
I created CXF-3097 to track this issue