https://bugs.winehq.org/show_bug.cgi?id=54268
--- Comment #2 from Jinoh Kang jinoh.kang.kr@gmail.com --- Fixed in 36ca172e85bf518faab581cc9b849fc79cfe6819.
It should be noted that the commit above is an application-side fix, not a system-side one. It is likely that there still is a bug in USER that can be exposed by other applications.
However, for Wine regedit's case, I suspect that the issue actually lies in the incomplete implementation of DeferWindowPos, which is currently non-atomic. My speculation is that 33617af8145b6fadfe41d48968a728ff57b3064b merely aided in exposing existing redraw/repaint bugs that were previously masked due to over-repainting.
I'll try to put together a test case for user32 that can reproduce the same bug to make sure it isn't lost.
Also, this bug was previously reported as bug 54137. I dropped it in favor of this due to likely invalid diagnosis.