Why can't C# infer type from this seemingly simple, obvious case

Given this code:

class C
{
    C()
    {
        Test<string>(A); // fine
        Test((string a) => {}); // fine
        Test((Action<string>)A); // fine

        Test(A); // type arguments cannot be inferred from usage!
    }

    static void Test<T>(Action<T> a) { }

    void A(string _) { }
}

The compiler complains that Test(A) can't figure out T to be string.

This seems like a pretty easy case to me, and I swear I've relied far more complicated inference in other generic utility and extension functions I've written. What am I missing here?

Update 1: This is in the C# 4.0 compiler. I discovered the issue in VS2010 and the above sample is from a simplest-case repro I made in LINQPad 4.

Update 2: Added some more examples to the list of what works.