Major Description
Many use cases assume that onCallback will be invoked with type FINALIZE when leadership is lost so that there is an opportunity to clean up. However, this is not the case, and the previous leader has no idea that it's not leader anymore.
Long term the right thing to do is to split onCallback into 3 different methods, but for now, we should also invoke onCallback with the appropriate type, since this seems to be the expected behavior.