The following call sequence causes QWindow to no longer deliver QEvent::UpdateRequest:

1. QRhiSwapChain::setWindow(window)
2. QRhiSwapChain::createOrResize()
   1. QD3D11SwapChain::createOrResize()
      1. QDxgiVSyncService::registerWindow(window)
3. QWindow::requestUpdate()
   1. QWindowsWindow::requestUpdate()
      1. QDxgiVSyncService::registerCallback()
   2. QWindowPrivate::updateRequestPending = true;
4. QRhiSwapChain::destroy()
   1. QD3D11SwapChain::destroy()
      1. QDxgiVSyncService::unregisterWindow(window)
5. (Since the window has been removed from the QDxgiVSyncService's window list, QPlatformWindow::deliverUpdateRequest() for that window will not be called.)
6. Further QWindow::requestUpdate() calls...
   1. Update request is pending, so do nothing.

This issue only occurs when QRhi is using the D3D11 or D3D12 backend.