There is a slight inconsistency in the way that getDataResourcePropertyDocument and the XML realisation's get 
GetCollectionPropertyDocument define responses. 

The WS-DAI getDataResourcePropertyDocument defines the following response:

<wsdl:message name="GetDataResourcePropertyDocumentResponse">
<wsdl:part name="GetDataResourcePropertyDocumentResponse" 
              element="wsdai:GetDataResourcePropertyDocumentResponse"/>  </wsdl:message>

It uses a GetDataResourcePropertyDocumentResponse type to wrap the document returned to the client. The 
GetCollectionPropertyDocument defines the following response:

<wsdl:message name="GetCollectionPropertyDocumentResponse">
      <wsdl:part name="GetCollectionPropertyDocumentResponse" 
                 element="wsdaix:XMLCollectionPropertyDocument" />
    </wsdl:message> 

This returns the XMLCollectionPropertyDocument type as opposed to wrapping it using a response type. Perhaps a change 
should be made enforce consistency.
.