I've noticed several iPad cases have magnetic clasps or similar. Which sounded great until I read a review of the Eco-Vue that mentioned the magnetic strip interfered with the functioning of the compass in the 3G model. Has anyone else experienced this problem with cases that have magnets? How big a problem is it? Does it interfere with GPS functions? I'd particularly like to know for the Eco-Vue as I'm seriously considering it and that's the one thing that would be a deal-breaker.