The async bit is totally a bug we should fix.

As for notify callback; in order to call an observer method, you need to know what bean it belongs to because you then need to retrieve the respective bean from context (or create it) and invoke it. The information we get from reading the method is insufficient for that. If we try to get the bean based on just class we might blow up with ambig. or unsatisfied dep. The bean can be @Typed or can have qualifiers or you can simply be looking not for this bean but some other extending it.
Therefore, you as a programmer are the only person who really knows what callback to invoke for sure.
It might be worth a spec issue to improve the docs in this regard - to specifically state that callback must be set even if you do read().