Torn off menus have no titlebar anymore, no way to close or move

int main( int argc, char *argv[] )
{
    QApplication app( argc, argv );
    app.setQuitOnLastWindowClosed(true);

    // Create Top Level MainWindow
    auto mainWindow = new QMainWindow();
    mainWindow->setAttribute(Qt::WA_DeleteOnClose);
    mainWindow->setWindowTitle(QString("Tear-Off Menu Test - Qt%1.%2.%3").arg(QT_VERSION_MAJOR).arg(QT_VERSION_MINOR).arg(QT_VERSION_PATCH));

    // Add menu to main menubar
    auto testMenu = mainWindow->menuBar()->addMenu("Test Menu");
    testMenu->setTearOffEnabled(true);
    testMenu->addAction("Action 1");
    testMenu->addAction("Action 2");

    mainWindow->resize(800, 600);
    mainWindow->show();

    /* The issue can also be reproduced by mimicking what QMenu internally does 
    for creating the QTornOffMenu. */
    /*
    auto menuWithTitlebar = new QMenu();
    menuWithTitlebar->addAction("Action 1");
    menuWithTitlebar->setWindowTitle("Tear-Off Menu");
    menuWithTitlebar->setParent(mainWindow, Qt::Window | Qt::Tool); // <- this call doesn't seem to work as in the past
    menuWithTitlebar->setAttribute(Qt::WA_DeleteOnClose, true);
    menuWithTitlebar->show();
    */    

    // Run Qt message loop
    return app.exec();
}