Explicit casting of enum -- intentional restriction?

[Namespace via Digitalmars-d-learn]

The Code below still works, so I guess it's some problem with the 
constraint of "exists".

----
import std.stdio;

enum Foo
{
	A = "B"
}

void test(string a)
{
}

void main()
{
	test(Foo.A);
	Foo.A.test();
}
----