If you configure WS-RM and WS-Security in the WSDL the server appears to combine the WS-RM sequence acknowledgement and response from the service into the same message and send it to the client's decoupled endpoint. As the client is only expecting to receive sequence acknowledgement messages on the decoupled endpoint not the result of the service invocation it can't correlate the response properly, and so retries sending the invocation to the server.
To run the test case just do:
mvn clean install
mvn -Pserver in one terminal and mvn -Pclient in another terminal.