QMenu::aboutToShow doesn't send on use appmenu

Minimal example:

#include <QtCore>
#include <QtWidgets>

int main( int argc, char** argv )
{
    QApplication a( argc, argv );
    QMainWindow w;

    QMenu* m = w.menuBar()->addMenu( "File" );
    m->addAction( "New" );
    QObject::connect( m, &QMenu::aboutToShow, [](){ qDebug() << "aboutToShow"; } );

    w.show();
    return a.exec();
}

If call 'w.menuBar()->setVisible( true );' to force show menubar inside a window than 'aboutToShow' will send.