(In reply to Fabian Maurer from comment #0)
> System the bug was tested on:
> - Arch Linux 64bit
> - Linux 4.19.08, AMDGPU driver
> - Mesa 17.2.0-devel (git-ccf9669cc1) / Mesa 17.0.5
> - Radeon R9 285
> - KDE Plasma 5 with OpenGL compositor and regular X session

Please test with a more recent version of Mesa before reporting bugs, otherwise
you are just wasting the time of developers (we already have limited
resources). You have an extremely odd setup, cutting edge Kernel with obsolete
Mesa versions (almost 2 years old).

Please retest with Mesa git or at the very least Mesa 18.3.