WSDL retrieved from the Web Service Proxy using ?wsdl URI differ

If you follow the instructions in the DataPower documentation, you can enable the HTTP GET and HEAD methods on the Front Side Handler for your Web Service Proxy, and you may expose a WSDL from within a Web Service Proxy with the ?wsdl URI. For example:
http://host:port/URI?wsdl
However, the retrieved WSDL may be different from the original WSDL that was uploaded to the Web Service Proxy (or the WSDL that the Web Service Proxy retrieves from a remote location).