Results of Web Method differ from server to client.

I am using a web method that returns a list of objects of type User.  I put a stop point while debugging in the web method (at the return statement) and a stop point in the Reference.cs on the client file where control is returned from the web method.  At the return statement in the Web Method, there are X number of User objects in the list. At the stop point in the Reference.cs file, there are 2X number of objects in thse list -- every object is duplicated.  There is absolutely NO processing code called (of course) between the WebMethod and the Reference.cs file on the client.  Has anyone encountered this problem?  I am racking my brains out trying to figure out why there are always twice as many objects when the result is returned to the client.

FYI - we are using XML serializable objects as return types.

Any help provided is very much appreciated.

-- Kim