Spurious window detail level changes in mixed-DPI setup
I am running gnome-shell 3.30.2 and mutter 3.30.2 on a mixed-DPI setup, consisting of a left primary LG Ultra HD 24" 3840x2160 monitor scaled to 200%, and a right secondary Dell P2414H 1920x1080 monitor scaled to 100%, under a Gnome Wayland session. The fact that it detects DP-1 as "monitor 2" and DP-2 as "monitor 1" is for another issue I'll probably file.
Anyway, after a random interval, sometimes triggered by the screen locker kicking in, all dynamically sized GTK 3 windows, which resize when dragged between monitors, that have been left on the 200% scaled monitor, will end up blurry, like they shifted to 100% scale and then got bilinear upscaled to 200% again. This happens to Gnome Terminal, Evolution, and the Files browser:
Upon moving it to the 100% scale display, it maintains the same image, but shrinks:
And upon moving it back to the 200% scale display, it grows back again, and regains the correct rendering detail:
It usually falls back to the first screen shot after an indeterminate time, again, possibly triggered by the screen locker.
AMD Radeon RX 480, using amdgpu/radeonsi, in case that matters.