Each ws endpoint deployment is associated with a Bus instance. That bus is saved as thread default bus into the thread that serves a given invocation to one of the deployment's endpoints. As a consequence this bus is also set when running the user code in the business methods of the endpoint. If the user creates a JAX-WS client in there, the JBossWS-CXF JAXWS Provider impl ends up leveraging the deployment (server side) bus instance instead of creating a new one.