[Win] qtbase/examples/opengl/2dpainting broken with TranslucentBackground

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    Window window;
    window.setWindowFlags(Qt::FramelessWindowHint | Qt::Dialog);
    window.setAttribute(Qt::WA_TranslucentBackground);
    window.show();
    return app.exec();
}