[Bug 55417] user32:msg - test_showwindow() sometimes fails due to an unexpected WM_SYNCPAINT message on Windows 10

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=55417

--- Comment #3 from Esme Povirk  ---
My best guess: A tooltip or other temporary window was displayed with
WS_EX_TOPMOST. The first ShowWindow call causes it to hide itself (for example,
if the mouse is no longer hovering over the owner of a tooltip), reveal some
part of the newly-shown window, and send WM_SYNCPAINT. The second call
processes sent messages before showing the window.

I'm not sure how to test that theory though.