HTTP Gateway and SOAPProcessor combination fails to handle MTOM messages in SOA-P 5

Issue

• We are using Http-Gateway and SOAPProcessor to expose our web services.
• We used JBoss webservice_mtom example and just replaced the jbr-listener with Http-Gateway:

<service category="Notification" name="MyMTOMService" description="..." invmScope="GLOBAL">
  <listeners>
    <!-- <jbr-listener name="JBR-Gateway" busidref="Http-1" is-gateway="true"/> -->  
    <http-gateway name="Http-Gateway" />
  </listeners>
  <actions mep="RequestResponse">
    ...
    <action class="org.jboss.soa.esb.actions.soap.SOAPProcessor" name="JBossWSAdapter">
     <property name="jbossws-endpoint" value="MTOMEndpoint"/>     
    </action>
    ...
  </actions>
</service>

• We get the following error:

WARNING [PhaseInterceptorChain] Interceptor for {http://webservice.webservicemtom.quickstart.samples.esb.soa.jboss.org/}MTOMService has thrown exception, unwinding now
org.apache.cxf.binding.soap.SoapFault: Error reading XMLStreamReader.
    at org.apache.cxf.binding.soap.interceptor.ReadHeadersInterceptor.handleMessage(ReadHeadersInterceptor.java:230)
    at org.apache.cxf.binding.soap.interceptor.ReadHeadersInterceptor.handleMessage(ReadHeadersInterceptor.java:60)
    at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:243)
    at org.apache.cxf.transport.ChainInitiationObserver.onMessage(ChainInitiationObserver.java:111)
    at org.apache.cxf.transport.servlet.ServletDestination.invoke(ServletDestination.java:99)
    at org.apache.cxf.transport.servlet.ServletController.invokeDestination(ServletController.java:431)
    at org.jboss.wsf.stack.cxf.ServletControllerExt.invoke(ServletControllerExt.java:173)
    at org.jboss.wsf.stack.cxf.RequestHandlerImpl.handleHttpRequest(RequestHandlerImpl.java:61)
    at org.jboss.soa.esb.actions.soap.SOAPProcessor.process(SOAPProcessor.java:212)
    at org.jboss.soa.esb.listeners.message.ActionProcessingPipeline.processPipeline(ActionProcessingPipeline.java:667)
    at org.jboss.soa.esb.listeners.message.ActionProcessingPipeline.processPipeline(ActionProcessingPipeline.java:614)
    at org.jboss.soa.esb.listeners.message.ActionProcessingPipeline.process(ActionProcessingPipeline.java:442)
    at org.jboss.soa.esb.listeners.message.MessageAwareListener$TransactionalRunner.run(MessageAwareListener.java:587)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)
Caused by: com.ctc.wstx.exc.WstxUnexpectedCharException: Unexpected character '-' (code 45) in prolog; expected '<'
 at [row,col {unknown-source}]: [2,1]
    at com.ctc.wstx.sr.StreamScanner.throwUnexpectedChar(StreamScanner.java:648)
    at com.ctc.wstx.sr.BasicStreamReader.nextFromProlog(BasicStreamReader.java:2047)
    at com.ctc.wstx.sr.BasicStreamReader.next(BasicStreamReader.java:1069)
    at com.ctc.wstx.sr.BasicStreamReader.nextTag(BasicStreamReader.java:1095)
    at org.apache.cxf.binding.soap.interceptor.ReadHeadersInterceptor.handleMessage(ReadHeadersInterceptor.java:122)
    ... 15 more