Ever since the last VLC update, I have this problem. I am using Ubuntu 18.04. In fullscreen, besides the video, VLC also shows Unity launcher (side bar) and the Ubuntu top bar (see the screenshot).
If I left click on the video, the bars disappear. But when I change the audio volume or pause the video, or move the mouse cursor, they reappear.
I have tried uninstalling VLC and installing it again, but the problem remains.
My specs are:
HP G5 255 (laptop) 15,6 inch 1080p display AMD A6-7310 APU with AMD Radeon R4 Graphics × 4 (1 GB allocated to iGPU) Gallium 0.4 on AMD MULLINS (DRM 2.50.0 / 4.15.0-39-generic, LLVM 6.0.0), Mesa 18.0.5 12 GB DDR3L 1600 MHz (4 + 8 GB) Ubuntu 18.04 64-bit, Unity 7
Screenshot: 
"Problem between Qt and Unity"? https://forum.videolan.org/viewtopic.php?f=13&t=147281&sid=350ff85f4dbb4339e3d100d3667d193d
