Do you have News Feeds or any other app that uses the webkit browser installed and running? I found that my browser did that when I used News Feeds. You can hold the Back button to exit the browser and re-open it and it will work, at least until you use News Feeds again. I ended up un-installing News Feeds because of it. I also play Forces of War, which must use the rendering engine or whatever as well, as it happens with that too sometimes.
