Consider the following code:

a.d:
class A {
  class Subclass { }
  protected void foo() { }
}

b.d:
class B : A {
  class Subclass : A.Subclass {
    void method() { foo; }
  }
}

Despite the fact that B.Subclass exists in a subclass of A twice over, this errors with:

b.d(6): Error: class `a.A` member foo is not accessible

It works if I write 'this.outer.foo'.

It also works if I *don't* inherit B.Subclass from A.Subclass.