Resolver fail to detect invalid method call

Considering a class "MyClass" having a string member "MyStringField".

The C# code below is invalid because method Sum<T>(Func<T,string>) doesn't exist.

IEnumerable<MyClass> myCollection;

var result = myCollection.Sum(myClassInstance => myClassInstance.MyStringField)

But the SyntaxEditor C# resolver say that "Sum" correspond to the extension method Enumerable.Sum<MyClass>(Func<MyClass,int>) and that variable "result" is of type "int" !?!