[int_19h]

You wouldn't even have to get lambdas involved for this problem to surface. Consider something like this:

   void Foo(double x) { ... }

   Foo(123);

This works, but now I add an overload:

   void Foo(decimal x) { ... }

and the above call is now ambiguous. Note that this example goes all the way back to C# 1.0!

Method overloading (and how it interacts with other language features) is probably the single most complicated part of C# today, for good reasons.