添加/更新Web引用时，防止在Reference.cs中生成代理类

I have a web service and a client. The classes used in parameters and return types are in a common DLL shared by both. However, whenever I update the web reference, visual studio generates copies of the classes with the same names and public properties and methods. Then the solution won't compile because the client code tries to use the versions in the common DLL. I can solve the problem by deleting the "duplicate" classes every time I update the web reference, and adding a using statement to point at the common dll's namespace. Is there a way to fix this permanently? I have a web service and a client. The classes