MTOM/XOP isn't enabled for JBossWS Native client

Issue

• We found that MTOM/XOP isn't enabled for WS client in JBossWS Native. By "MTOM/XOP not being enabled" here I mean that the client always sends "Content-Type: text/xml;" instead of "Content-type: multipart/related;" even though the configuration seems to be properly set up.
• The JBossWS Native client is deployed as a servlet on EAP 5 and invokes an external MTOM'ed web service.
• Basically what we've done to enable MTOM for WS client is as follow:

  SOAPBinding binding = (SOAPBinding)((BindingProvider)port).getBinding();
  binding.setMTOMEnabled(true);

• Can you tell me what's the problem? Am I just ignoring some important configuration, or is it a bug in JBossWS Native?
• We found JBPAPP-10697 but don't think it is relevant to this issue, as we are not using Native Dispatch client.