FFXIV depends on this. It calls SetFullscreenState when it receives WM_WINDOWPOSCHANGED. Through luck the recursion aborts after two calls. The user-visible bug is that after leaving fullscreen, the game's window is still TOPMOST because we overwrite the stored pre-fullscreen window flags.
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v4: dxgi/tests: Test nested SetFullscreenState from the same thread.
dxgi/tests: Test nested fullscreen application from different thread.
dxgi: Catch nested SetFullscreenState invocations.
dxgi: Unlock the wined3d mutex after storing the new target.
dxgi/tests: Run test_swapchain_window_messages on d3d12.
dxgi: Call wined3d_swapchain_state_set_fullscreen in d3d12_swapchain_init.
dxgi/tests: Run test_resize_target_wndproc on d3d12 too.
dxgi/tests: Fix UnregisterClass call in test_resize_target_wndproc.
https://gitlab.winehq.org/wine/wine/-/merge_requests/1964
This is what it looks like:

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v7: winecfg: Add an option to enable WinRT app dark theme.
https://gitlab.winehq.org/wine/wine/-/merge_requests/2183
On Thu Mar 9 18:05:24 2023 +0000, **** wrote:
> Marvin replied on the mailing list:
> ```
> Hi,
> It looks like your patch introduced the new failures shown below.
> Please investigate and fix them before resubmitting your patch.
> If they are not new, fixing them anyway would help a lot. Otherwise
> please ask for the known failures list to be updated.
> The tests also ran into some preexisting test failures. If you know how
> to fix them that would be helpful. See the TestBot job for the details:
> The full results can be found at:
> https://testbot.winehq.org/JobDetails.pl?Key=130422
> Your paranoid android.
> === w7u_2qxl (32 bit report) ===
> kernel32:
> loader.c:2324: Test failed: wrong tls data 'hello world' at 00C54600
> === w7u_adm (32 bit report) ===
> kernel32:
> loader.c:2324: Test failed: wrong tls data 'hello world' at 00BE4600
> === w7u_el (32 bit report) ===
> kernel32:
> loader.c:2324: Test failed: wrong tls data 'hello world' at 00C546A0
> === w7pro64 (64 bit report) ===
> kernel32:
> loader.c:2324: Test failed: wrong tls data 'hello world' at 0000000000D405F0
> ```
This is a regression in the tests when running on Windows 7.
That should have been grounds for rejection of the merge request!
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https://gitlab.winehq.org/wine/wine/-/merge_requests/2361#note_26599