Referring back to the Original Post, am I reading this correctly? The way it reads to me is that it sounds like the backlight for the Hardware keys is staying on dimly lit even when the power button is pressed to turn off the screen and lock the device?
So when the screen is off and completely black when the phone is in a non-awake state the keys are still lit dimly? And even after a factory restore? ...It kind of defies logic...
However, if this is the case ^ I'm led to think that there is a hardware issue going on. Has the phone been exposed to any water? Or maybe an overly moist/humid environment? Any drops or knocks to the front of the screen, particularly in the area just above the buttons?