Happened to me while purchasing an app a line appears on the keyboard. I have a feeling it's a bug I hope it is as I only notice this happening in when entering your pw when purchasing an app.
That is not why I am sure if my problem is the same or not. My situation is not limited to the App Store app. In fact I have never noticed it there.
On two occasions, my display went into full blown cardiac arrest mode. Yesterday I was watching a highlight reel on the MLB At Bat app. All of a sudden the whole screen started shaking. I stopped the video and the display continued to shake. The entire home screen was flickering. I powered off and on, but the problem continued. After a few minutes of non use, it stopped. I noticed flickering off and on throughout the day yesterday, but nothing as severe. The flicker would only last for a second or two.
Today my phone had been perfect until a I watched a long YouTube video. Then it did the same thing. The whole display started spazzing out again. I powered off and on to no avail. When it was booting up, even the white Apple logo was shaking. After a few minutes of non use, it stopped.
I have been trying to replicate the problem this evening but can't seem to. If it is a hardware issue, I would like to get the thing sent back. I don't want to go through the hassle of sending it back though if it is a software issue.
Not sure what to do at this point.