Thanks for your comment,
Because the Application features some image processing, where the QR FinderPatterns are used for rough localication of other objects placed nearby the QR-code. And if the evaluation of one preview frame takes up to 7s it's not possible to use debugging when testing for device movement respectivley we would have to move the phone really slow.
It's not a serious problem that limits functionality actually, but slows down development process and testing significant - and anoying ;)