[SFML 2.1 + WinApi] Czyszczenie okna usuwa kontrolki z ekranu.

WindowClass.style = 0;
WindowClass.lpfnWndProc = & OnEvent;
WindowClass.cbClsExtra = 0;
WindowClass.cbWndExtra = 0;
WindowClass.hInstance = hInstance;
WindowClass.hIcon = NULL;
WindowClass.hCursor = 0;
WindowClass.hbrBackground = reinterpret_cast < HBRUSH >( COLOR_BACKGROUND );
WindowClass.lpszMenuName = NULL;
WindowClass.lpszClassName = "x";
RegisterClass( & WindowClass );
hwnd = CreateWindow( "x", "x", WS_OVERLAPPEDWINDOW | WS_VISIBLE, 0, 0, 800, 600, NULL, NULL, hInstance, NULL );
button = CreateWindowEx( 0, "BUTTON", "Nasz przycisk", WS_CHILD | WS_VISIBLE,
100, 100, 150, 30, hwnd, NULL, hInstance, NULL );
ShowWindow( hwnd, nCmdShow );

app.create( hwnd );

SendMessage( hwnd, WM_SYSCOMMAND, SC_MAXIMIZE, 0 );
MSG Message;
Message.message = ~WM_QUIT;
while( Message.message != WM_QUIT )
{
   
    if( PeekMessage( & Message, NULL, 0, 0, PM_REMOVE ) )
    {
        TranslateMessage( & Message );
        DispatchMessage( & Message );
    }
    else
    {
        app.clear( sf::Color( 255, 0, 0 ) );
        app.display();
    }
}