Switchyard: Invoking outbound soap webservice with NTLM authentication fails

Issue

I am trying to invoke an external webservice using the following NTLM configuration in switchyard.xml:

    <sca:reference name="EngineSoap" multiplicity="0..1" promote="Route/EngineSoap">
      <sca:interface.wsdl interface="wsdl/test.wsdl#wsdl.porttype(EngineSoap)"/>
      <soap:binding.soap name="soap1">
        <soap:contextMapper />
        <soap:wsdl>wsdl/test.wsdl</soap:wsdl>
        <soap:endpointAddress></soap:endpointAddress>
        <soap:ntlm>
         <soap:user>user</soap:user>
         <soap:password>pwd</soap:password>
         <soap:domain>domain</soap:domain>         
        </soap:ntlm>
      </soap:binding.soap>
    </sca:reference>

However, the NTLM credentials are not being sent to the webservice and hence the authentication is failing. Upon inspecting a wireshark tcpdump we found out that the domain is correct but the username is not the one provided in the soap binding, but rather from the logged in Windows user.