By default, the proxy generated from Visual Studio transform a List to an array ... If ... as me ... you use WCF only in .NET ... you can easily generate proxy class ... Open a command shell, and type :

svcutil.exe http://localhost:8000/Tests/Service?WSDL /out:c:\generatedFile.map /ct:System.Collections.Generic.IList`1 /ct:System.Collections.Generic.IDictionary`2

With this line ... you generate proxy classes with generics ... :-)
Have fun !