ProxyGen fails: Dataset Parameters contain different definit

OS: Win 8.1 (64-bit), OE 11.5 (32-bit)

Proxy #1 uses following PDS definition:

define dataset dsReportOut{&ext}
  serialize-name "Reports"
  {&REFERENCE-ONLY}
  for ttReportOut{&ext}
.

Proxy #2 uses following PDS definition:

define dataset dsReportOut{&ext}
  namespace-uri "webservice.unit4.com/.../25"
  namespace-prefix "u4ns"
  serialize-name "Reports"
  {&REFERENCE-ONLY}
  for ttReportOut{&ext}
  .

When I try to generate a WSDL containing both proxies ProxyGen fails with "Dataset Parameters contain different definitions but same XML-NODE-NAME".

I expect ProxyGen to take namespace-uri and namespace-prefix into account or am I mistaken?