RS warning "Cannot resolve symbol" for ArgumentException, not case sensitive?

[6.0]

class FooBar
    {
        void Bar(FooBar fooBar)
        {
            //RS warns for unresolved symbol "foo"
            //throw new ArgumentNullException("foo");
            //No RS warning
            //throw new ArgumentNullException("FooBar");
            //No RS warning
            //throw new ArgumentNullException("foobar");

            //Expected only below to result in no warning from RS
            throw new ArgumentNullException("fooBar");

        }      }