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