I had something similar very briefly back in June after flashing a leaked MR2 RUU. When in landscape mode, the "A" key was very difficult to activate. It was more though in that the entire screen would periodically act like a ghost was touching it. It did this randomly for about a week, then went away and has never happened again. I figured it had something to do with the leaked RUU or that something had to settle in after flashing it. You could try recalibrating the touchscreen by going to Menu, Settings, Language & keyboard, Touch Input, Text Input, under Finger touch precision, choose Calibration tool or even Reset calibration. If it still happens, you may have a bad screen. Or you could try something as simple as a battery pull.
I may have a solution to this problem, it just worked for me. I have a thunderbolt which hadn't been dropped or abused but somehow parts of the screen stopped registering. I couldn't type well or use it for much and was offered a referb again but declined because i've had more than one issue with this phone. Anyways, after being told that I could get my date moved I got a new phone but wanted to see if i could fix this one. I watched this youtube video
and got the idea that it might just need the 3 ribbon cables between the screen and motherboard reseated. I took it apart to right before the complex part that you need to unglue anything and put it back together. Problem solved.
I find this unfortunate that they don't keep techs in the store to perform this kind of easy fix...
Still getting something else (htc rezound) but now i have an extra or can sell this for some of the price difference in the upgrade.
I've use lighter electric to solve the problem
If you have a lighter that use electric to fire it up,you only need to take the letric thing's
And use that to dead spot area and now you can touches all screen area.