Into the Breach rendering stalls if vertically truncated (590380)

Compatibility Report

• Name of the game with compatibility issues: Into The Breach
• Steam AppID of the game: 590380

System Information

• GPU: Ivybridge / Radeon HD 6310
• Driver/LLVM version: Mesa 18.2.7/6.0.1
• Kernel version: 4.19.10 (Ivybridge) and 4.14.82 (Evergreen)
• Link to full system information report as Gist:
• Proton version: 3.7-8, 3.16-4, 3.16-5 Beta

I confirm:

• that I haven't found an existing compatibility report for this game.
• that I have checked whether there are updates for my system available.

Symptoms

When running Into The Breach on Gentoo + Mate (software compositing enabled), the game renders fine on the test boxes here that have discrete vram, but stalls when on an integrated graphics system. I can get the game to render a couple more frames every time I alt-tab in and out of the game. If I disable software compositing in Mate's settings, the game no longer refreshes the rendered frame on alt-tab.

The rest of the DE and other applications remain responsive throughout testing and the game maxes out one cpu core. Nothing of real interest in the proton log spew.

I've been seeing this behavior since the initial release of Proton.

Reproduction

Run Into The Breach on Mate (1.18) and an integrated graphics system.

Start by reproducing Into The Breach on MATE with integrated graphics, comparing software compositing enabled and disabled as described. Check whether the stall still occurs with the reported Proton versions and hardware configurations; done means the game continues rendering without requiring alt-tab. No source file or test is named in the report.