Video Playback with system/desktop in background on the Official 7″ Display

Hello!
I am currently building a Kodi setup with a Raspberry Pi 3 and the official 7″ touchscreen for a car project. I already had problems with its shutdown process but I was able to solve those thanks to @rascas over on this thread. I installed the Raspbian Jessie with Pixel version from 2017-04-10 and installed Kodi via apt-get. The touchscreen itself does work and so does displaying the menus but when I start playing back a video that does not fit the screen like movies with cinema aspect ratio, instead of black borders I can see the desktop in the background, which does not look good. I also tried booting Raspbian up in console mode but then you can simply see that in the background. I also tried hooking the Pi up to an HDMI screen for testing purposes and there the movies play back just fine.
I would be very glad if someone could help me with fixing this issue and if you need more information skim my old thread or simply ask me and I will try to provide it!

Zurafta