I've been having the same problem for about two months now. I re-calibrated the screen, but that didn't help. I even did a factory reset and still had the same problem. I took it to the store a few weeks ago, and of course there was nothing wrong with my phone when I tried to show the guy. He told me that if I keep having the problem to call customer service and get a replacement device since it's still under warranty.

Rawchell