Carefull with Event.ADDED_TO_STAGE and Event.REMOVED_FROM_STAGE

Use these events very carefully because the Flex Container class re-parents children. This is done during resizing. The Container class which is the super class of HBox/VBox etc tries to create scrollbars and in the process creates something called contentPane. Here is the method in the Container class that does the reparenting...

mx_internal function createContentPane():void {
    ....
    ....
    ....
        for (var i:int = 0; i < n; i++)
        {
            // use super because contentPane now exists and messes up getChildAt();
            var child:IUIComponent =
                IUIComponent(super.getChildAt(_firstChildIndex));
            newPane.addChild(DisplayObject(child));
            child.parentChanged(newPane);
            _numChildren--; // required
        }
}

The above code results in firing the Event.REMOVED_FROM_STAGE and Event.ADDED_TO_STAGE. This can be dangerous if you are relying on these events to do something critical like destroying the view or its associated controllers etc. I have also seen implementations where a view listens to these methods and calls a dispose method to remove listeners, unwatch bindings and cleanup memory.

In short, these events become unreliable.