Mac : Calling showFullScreen() then showNormal() on a widget results in top menu hiding.

#include <QtGui>

class MainWindow : public QMainWindow
{
   Q_OBJECT

public:
   MainWindow();

public slots:
   void testSlot();
   void testSlot2();

private:
   QByteArray geo ;
};


MainWindow::MainWindow()
   : QMainWindow()
{
//   QTimer::singleShot(1000, this, SLOT(testSlot()));
   QTimer::singleShot(2000, this, SLOT(testSlot2()));
}

void  MainWindow::testSlot()
{
   show();
   showFullScreen();
};

void MainWindow::testSlot2()
{
   showNormal();
};


#include "main.moc"

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

   MainWindow mainWindow;
    mainWindow.show();
    mainWindow.showFullScreen();

   return app.exec();
}