child QSystemTrayIcon of QApplication causes an error, when the application finished.

#include <QMainWindow>
#include <QSystemTrayIcon>
#include <QIcon>
#include <QPixmap>
#include <QObject>


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    
    QMainWindow w;
    w.show();
    
    // icon
    QPixmap pixmap(22, 22);
    pixmap.fill(Qt::green);
    QIcon icon(pixmap);
    
    // Case 1 : OK
//    QSystemTrayIcon trayIcon;
//    trayIcon.setIcon(icon);
//    trayIcon.show();
    
    
    // Case 2 : Error.
    QSystemTrayIcon* trayIcon = new QSystemTrayIcon(&a);
    trayIcon->setIcon(icon);
    trayIcon->show();

    // Case 3 : OK
//    QObject* object = new QObject(&a);

    return a.exec();
}