Not possible to grab QEvent::NonClientAreaMouseButtonRelease

#include <QtGui>

class DockWidget : public QDockWidget
{
public:
	DockWidget(QWidget *parent) : QDockWidget(parent)
	{
	}
	
	bool event(QEvent *event)
	{
		if (event->type() == QEvent::NonClientAreaMouseButtonRelease) {
		qDebug() << "button release";
		}
		if (event->type() == QEvent::NonClientAreaMouseButtonPress)
		{
			qDebug() << "button press";
		}
		return QDockWidget::event(event);
	}

};
class MainWindow : public QMainWindow
{
	Q_OBJECT
public:
	MainWindow()
	{
		DockWidget *dock1 = new DockWidget(this);
		addDockWidget(Qt::TopDockWidgetArea, dock1);
		
	}

	bool event(QEvent *event)
	{
		if (event->type() == QEvent::NonClientAreaMouseButtonRelease) {
		qDebug() << "mainwindow release ";
		}
		if (event->type() == QEvent::NonClientAreaMouseButtonPress)
		{
			qDebug() << "mainwindwo press";
		}
		return QMainWindow::event(event);
	}

	




public slots:

	void testSlot()
	{
	}


};


#include "main.moc"

int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    MainWindow box;
    box.show();
    return app.exec();    
}