I was looking for answers on the Internet to fix the issue with the distance sensor - while talking the screen sometimes erratically switches on and you can accidentally end the call  with your cheek. This can be fixed by re-calibrating the distance sensor. 

To enter the test menu use the same code as for the other models in the 9500 family: 
1. Open Phone call menu [as if you would call someone]
2. click the manual dial menu [at the bottom]
3. key in this code:     *#87# 
4. The factory menu should open [you will know when you see it]
5. On this screen select MMI2 or MMI4    [this is where it differs from other models]
6. Select Single Test
7. Find and select Distance Calibration [color=#2980b9][about the middle of the screen][/color]
8. Follow the instructions on the screen. A demonstration how to do it can be found here:
 

Hope this is useful for someone, 
Regards

All credit to the guy who made the YT video!

Good! Good! Good!