[Bug 55539] New: user32:msg test_hvredraw fails in win1709 with unexpected region

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=55539

Bug ID: 55539
           Summary: user32:msg test_hvredraw fails in win1709 with
                    unexpected region
           Product: Wine
           Version: 8.15
          Hardware: x86-64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: user32
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

win1709_newtb-w1064v1709-64 now consistently fails in test_hvredraw with
mismatched regions. This failure appears to have been introduced by
https://gitlab.winehq.org/wine/wine/-/commit/fa038c3c3714cd1293e4de6aad44c14...,
as it was the only change when this test started failing.

There are 34 total failures that look somewhat like this:
msg.c:9655: Test failed: SimpleWindowClassWithHRedraw 00cf0000 SetWindowPos
redraw #1 (0, 0, 50, 0): Update region shall match expected region
msg.c:9655: Test failed: SimpleWindowClassWithHRedraw 00cf0000 SetWindowPos
redraw #2 (0, 0, 50, 50): Update region shall match expected region
msg.c:9655: Test failed: SimpleWindowClassWithHRedraw 00cf0000 SetWindowPos
redraw #3 (0, 0, -50, -50): Update region shall match expected region
msg.c:9655: Test failed: SimpleWindowClassWithHRedraw 00cf0000 SetWindowPos
redraw #5 (-50, -50, 50, 0): Update region shall match expected region

I did a test run with some traces, and it seems the actual update region always
matches the window's visible area. It's not clear to me why running the test in
a temporary desktop would cause this.