One of the permanent features on an iPhone turns off the screen (display and the touch receptors) when during a phone call you press the screen against your ears and cheek. The screen would almost instantaneously turn itself completely "on" when the phone would move away from the cheek and ears.
This at least was the case before iPhone 5. On my iPhone 5, the screen sometimes does not turn off or turn back on. I can confirm that iOS6 has nothing to do with this --my old iPhone 3GS on iOS6 does not face this problem.
Following the recommendations of this post, I went to the Apple Store but they just replaced my iPhone 5 when I demo'd the problem to them. The new iPhone 5 unfortunately has the same problem --even with factory settings.
Does anyone know of a way to solve this problem or am I just unlucky to get two defective iPhone 5s in a row and should try my luck again?
P.S.:- I am not using any cases, covers, screen coats or any other accessories.