Hello,
i have some Problem with proximity sensor, when i receive a call, or if i am calling someone, the Screen turns immediately off, i found out that this could be a sensor issue. i tried this:

the state is always at close, when im closing the sensor with a finger nothing happens, if try it some more time it may go to open state. Than it turns immediately back to close state or it stay some time in the open state.

I have this phone for second day, i didn't install anything from extra repository, i just made an sytsem update with wlan