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.