https://bugs.winehq.org/show_bug.cgi?id=56149
--- Comment #2 from Gabriel Ivăncescu gabrielopcode@gmail.com --- The reason it "worked" before the blamed commit is because it was actually broken when it comes to a fullscreen virtual desktop, it didn't remove the decorations when it was actually fullscreen at all.
So when the game resized the VD to a lower resolution, it simply kept the decorations that were never removed in the first place.
Obviously, it should add the decorations back on a resize, not sure why it doesn't.
Also while testing this I found another issue: if you set the virtual desktop to less-than-fullscreen in winecfg such as 800x600, and then use "wine explorer /desktop=foo,1920x1080" (assuming that's your fullscreen resolution), the created desktop will cover the whole screen, but not the taskbar. I can confirm that having it set in winecfg to 800x600 is the issue, because if it's not set to a virtual desktop at all, or it's set to 1920x1080 as well, it works as expected.