The PureMVC Framework Code at the Speed of Thought

I build this and its running fine. Now I have a question to the NotificationInterests of the customStack ChildMediator. I've created this Mediator within the CustomStackMediator:
private function onChild1Created ( event:Event = null ):void
{
      facade.registerMediator( new Child1Mediator( customStack.child1 ) );
}
In the Child1Mediator i've set some NotificationInterests, but it seems, that the Interests will be ignored.
What is my problem - is the Child1Mediator not correctly registered or is it not possible because it's initializied within the CustomStackMediator?

Can I solve this with facade.registerObserver? This produces an error message because the method is not defined. How to define this, i couldn't find any example.