stage.stageWidth and stage.stageHeight refer to the full rectangular region where AIR renders its content to the screen. stage.width and stage.height refer to the dimensions of whatever children the stage happens to contain, and if any of those children are moved or resized, stage.width and stage.height will be updated. You want to use stage.stageWidth and stage.stageHeight here, as I suggested in my previous post.
the Event.RESIZE gets fired 2 times, I just do not understand why!
I don't think there's anything special to understand here. That sort of thing can happen. Maybe Android resizes its window twice for some random, obscure reason, and AIR just does its best to pass on those changes to us in a new Event.RESIZE each time.
I always simply listen to Event.RESIZE on startup and adjust my app's layout any time that the native stage resizes. This allows for device orientation changes, going into and out of full screen, windows resized by users (in desktop apps, obviously, for that last one). You don't even need to start a new Starling instance. It's possible to adjust its view port and stage dimensions after it has already started. Starling's stage then dispatches its own resize event and you can change the layout however you want.