I face this problem everywhere indoor outdoor bathroom kitchen everywhere. I am sure proximity sensor is faulty. I can not claim warrenty aswell. I tried to check if proximity sensor is working by some command that returns open or close. it always returns close. yeah sometimes it works and that too in kernal op.. not in power. so I am pretty confident that nothing else will be of any use exept a hack to unlock phone when locked by incoming call. later I can install slide to answer for inpoket problem.