According to the Resteasy documentation, the Resteasy Built-in Internally-Thrown Exceptions section , the exception _:
o.j.r.plugins.providers.jaxb.JAXBMarshalException is mapped with the Status code 500.
http://docs.jboss.org/resteasy/docs/2.0.0.GA/userguide/html/ExceptionHandling.html
This of course happens when NO Exception mapper is available. Unfortunalty this does not seems to be correct , as a Status 200 is set to the Response , after debugging , the Status 200 is defined in HttpServletResponseWrapper.
This happens if a Post of a malformed xml request (Upon POST),ideally it may be a BAD_REQUEST (400)