mobile

Hello everyone, first of all I did a search on this topic, but either I am too stupid to do a proper search or there hasn't been any problem like mine yet. :eek:
I also did a little video, check it out.

https://youtu.be/lB3gYQUyL_8

Whenever I get a call or make a call myself (and the moment I press the dial button) the screen blacks out. This may be a solid and reasonable feature when holding
your phone to your ear to not accidently start any other app with it. The problem is that the display stays dark no matter if I put it to my ear or not. It is like the sensor is registering some
sort of object in front of it and therefore gets into "ear on the phone-display shutdown mode". First I thought the sensor was messed up, but then it still seems to differentiate between
daylight and nighttime, because the screen gets darker when covering the sensor with my finger and lights up when I remove it from that spot.
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When accidently having called someone and I want to stop the call, the display had turned black of course, so no way to shut down the call. So I start pressing buttons, like the middle menue button,
and I get to the desktop screen. Still need to shut down the call, so I want to go to the infopanel (upper slide down menue) and the moment I start moving my finger down, to enter the call panel, it immediatly gets dark again.
But there are times when I can access the upper infopanel (without the screen turning black) and see my call being there, but the instant I press on the entry the screen turns black.
Only solution is to quickly remove the battery to shut down that call.
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I have put on a display protector, but it doesn't cover any sensors really.
The problem started with installing CyanogenMod11 and persisted with the latest CyanogenMod12.

Any idea what I can do?

My current install:

Cynaogenmod-Version:
12-20150407-Nightly-jfltexx

Model:
GT-i9505

Android Version:
5.0.2

Baseband:
i9505XXUGNG8