Ever since I got my iPhone 5S, whenever I decline a call by pressing the power button twice, the touchscreen becomes unresponsive until I lock the phone and then unlock it again. I have always thought this is a bug in iOS but now that almost half a year has passed, I am beginning to think my phone is somewhat at fault. I have restored it since and even set it as new a couple of times but to no avail. Do you guys have the same problem or not? My iPhone is the 32GB unlocked european version. Thanks!