QMessageBox with standardButtons == QMessageBox::NoButton don't react on signal close()

#include <QtGui/QApplication>
#include <QMessageBox>
#include <QTimer>

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

    QMessageBox w( QMessageBox::Information, 
        QObject::tr("QMessageBox test"),
        QObject::tr("This message box should be closed in 5 s" ));
    w.setStandardButtons(QMessageBox::NoButton);
    w.show();
    QTimer::singleShot( 5000, &w, SLOT(close()) );
    return a.exec();
}