Custom request mapping for SOAP call, how is this supposed to work?

I am using a custom request mapping when calling a SOAP webservice. Results are not as expected.

When I insert

<![CDATA[<]]>

into one of the parameters, the resulting XML will contain:

< instead of what I inserted.

So it seems like Mendix parses my resulting request, and rebuilds the XML using its own way of escaping. Is this indeed what happens?

Am I right that is is simply a bug, as the whole point of using a custom mapping is to be in full control of the resulting XML?