[Bug 53434] user32:msg - test_SendMessage_other_thread() sometimes fails on Windows 10 1507 - 1909

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=53434

--- Comment #1 from François Gouget  ---
This case can have some more related failures and more Windows 10 versions are
actually impacted.

For instance on 2022-08-05 w1064v1809-32:

msg.c:18486: main: call SendMessage
msg.c:18493: main: call PeekMessage
msg.c:18495: Test failed: expected WM_USER+1, got 031f
msg.c:18497: Test failed: SendMessage from other thread 3: 1: the msg sequence
is not complete: expected 0401 - actual 0000
msg.c:18497: Failed sequence SendMessage from other thread 3:
msg.c:18497:   0: expected: msg 0403 - actual: MsgCheckProc: 00030366 0403 wp
00000000 lp 00000000 (flags 19)
msg.c:18497:   1: expected: msg 0401 - actual: nothing
msg.c:18505: Test failed: wrong status 00080000
msg.c:18507: main: call PeekMessage
msg.c:18508: Test failed: PeekMessage should fail

Where 0x031f == WM_DWMNCRENDERINGCHANGED?

And on 2022-04-28 cw-gtx560-2009-64:

msg.c:18418: main: call GetMessage
msg.c:18420: msg.c:18347: thread: call SendMessage
Test failed: expected WM_USER, got 031f
msg.c:18422: Test failed: SendMessage from other thread 1: 1: the msg sequence
is not complete: expected 0400 - actual 0000
msg.c:18422: Failed sequence SendMessage from other thread 1:
msg.c:18422:   0: expected: msg 0402 - actual: MsgCheckProc: 0000000001C7072A
0402 wp 00000000 lp 00000000 (flags 19)
msg.c:18422:   1: expected: msg 0400 - actual: nothing
msg.c:18431: main: call SendMessage
msg.c:18438: main: call PeekMessage
msg.c:18440: Test failed: expected WM_USER+1, got 0400
msg.c:18442: Test failed: SendMessage from other thread 3: 1: the msg 0x0401
was expected, but got msg 0x0400 instead
msg.c:18442: Failed sequence SendMessage from other thread 3:
msg.c:18442:   0: expected: msg 0403 - actual: MsgCheckProc: 0000000001C7072A
0403 wp 00000000 lp 00000000 (flags 19)
msg.c:18442:   1: expected: msg 0401 - actual: MsgCheckProc: 0000000001C7072A
0400 wp 00000000 lp 00000000 (flags 19)
msg.c:18450: Test failed: wrong status 00080000
msg.c:18452: main: call PeekMessage
msg.c:18453: Test failed: PeekMessage should fail