Until this bug is fixed.
The ONLY workaround I have been able to find is to:
Generate the class with clearing the checkbox for the undocumented option
“Serialize XML AnyType struct/array members as strings (uncheck for legacy behaviour).”
Which as far as I can see actually should read “Render XML and return Struct (uncheck to return XML handle)”.
Then manually render the XML...
So no fun, but when you are stuck...
Cheers
Marco