I believe that I have discovered an issue around MTOM/XOP SOAP response
generation. I have tested Metro 1.1. and 1.4 with Firefox 3.6 and IE8.
It could be also a browser issue.
The problem is the Content-Type HTTP response header. It seems to be not parsed
in the browser xhr object properly resulting in XML response null.
(http://www.w3.org/TR/soap12-mtom/ 3.2. Serialization of a SOAP message)
In the header there comes something like this: