i think you misunderstood me a little bit. that the screen disapears while i hold it on my ear is normal and a good think, like you mentioned, but my display gets black while making a phone call and holding it in my hands (e.g. to use the external speaker).

What i didnt mentioned before is that, after the other person has hang up, the screen still stays black and i have to unlock my phone (swipe to unlock). yes, its locked then... remember, i made the phone call and unlocked the device before