This works for anything running in "Game Mode", and it looks like this:
All windows-related programs (Explorer, dwm, task manager...) lock up. Some lock up in strange ways, task manager only locks up if you change tab, move/resize the window, or press any key, but mouse doesn't seem to break it.
The only way to fix the issue is to Alt+F4 the game, and for games which ask "ARE YOU SURE" and require you to click OK, you can't do anything, because the giant alt+tab window is sitting over the game. So for these I have to restart my computer, because task manager freezes. It's really derp.
i5-2500k, 550ti, 16gb ram, 120gb ssd
procaster 20.3 (latest?)