Comment # 8 on bug 109331 from andrew.m.mcmahon@gmail.com

My system has changed somewhat since writing this bug report. 

As all Feral games on STEAM officially support either STEAMOS or Ubuntu; I
thought I'd check out xubuntu 18.04 LTS - specifically:
https://pastebin.com/f8cTGLSY

The same glitch appears with the current Mesa drivers provided by the
distribution (18.2.8)

But using oibaf's ppa:
https://launchpad.net/~oibaf/+archive/ubuntu/graphics-drivers

Mesa related packages are updated to:
Mesa 19.1.0-devel (git-54522d0 2019-03-06 bionic-oibaf-ppa)

And I can no longer reproduce the issue! https://i.imgur.com/VhIylSp.jpg

As I've made no other changes other than switching Mesa packages I can only
assume that this has been fixed by an update/commit recently.

Many thanks to everyone who works on Mesa.
In just a few years (since I last tried Debian) my R9 285 has gone from having
no support whatever in Linux to being very capable indeed to the point where I
no longer require Windows: https://imgur.com/a/keUM4VS
https://imgur.com/a/awddkUg