WSDL generation in IS releases prior to 7.1 has many shortcomings. For IS 6.x releases, I would create your WSDL first in a third-party tool such as XML Spy Enterprise or the new Eclipse WSDL editor and then create services that can be invoked with messages created from the WSDL.
The IS 7.1 FCS release has a completely redesigned WSDL creation capability (called a Web Services Descriptor) node that supports WSDL-first as well as generation of Flow from WSDL’s from other parties. The new WSD node contains built-in WS-I interoperability testing that can be run on WSDL’s from partners or ones generated for IS-provided services.
Very easy to use, very capable and, yes, long, long overdue!