I'm not sure how to describe this exactly... My Hero is really laggy a lot of the time, especially when I'm running Sprint Navigation, as I was when this happened. When I bring up menus and settings, sometimes it randomly flips through selections and if I select something, it acts as if I made a different selection. So, I have no idea what my phone thinks I did, exactly, but now when I first unlock my phone or exit an application, a large transparent dark gray rectangle appears overlaying the bottom fifth of the screen, above the Phone bar, covering the first row of icons. It reads simply "Z", and it goes away in a few seconds. I can't click on it - touching it selects the icons behind the bar. Anybody know what this is or how to make this go away?