Alias this and inheritance

[Aurelien Fredouelle via Digitalmars-d-learn]

The following code does not compile:

struct S { }
class A
{
  S s;
  alias s this;
}

class B : A
{
}

void main()
{
  A asA = new B;
  B asB = cast(B)asA;
}

I would expect the last line to successfully cast the B instance 
I created back into type B, however this seems to be preempted by 
the alias this:

Error: cannot cast expression asA.s of type S to app.B

Is there a way to force this cast to operate on the object of 
type A instead of automatically using A.s?

Thanks,
Aurelien