Cosmetic pen with opengl rendering

[spepegiuqt]

Hi all,
I try to set the cosmetic pen for QGraphicsPolygonItem but if I use the opengl render it doesn't work as I expect.
Here the code:

scene.setSceneRect(-0.0005,-0.0005,0.001,0.001);
 
	QPen pen;
	pen.setColor(QColor(Qt::red));
	pen.setCosmetic(true);
 
	QPolygonF polyF;
	polyF << QPointF(0.0002,0.0002)
			<< QPointF(0.0003,0.0002)
			<< QPointF(0.0003,0.0003)
			<< QPointF(0.0002,0.0003);
 
	QGraphicsPolygonItem* polyItem = new QGraphicsPolygonItem(polyF);
 
	polyItem->setPen(pen);
 
	scene.addItem(polyItem);
 
	ui->graphicsView->setBackgroundBrush(Qt::black);
	ui->graphicsView->setCacheMode(QGraphicsView::CacheBackground);
	ui->graphicsView->setRenderHint(QPainter::Antialiasing);
	ui->graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
	ui->graphicsView->setScene(&scene);

scene.setSceneRect(-0.0005,-0.0005,0.001,0.001);

	QPen pen;
	pen.setColor(QColor(Qt::red));
	pen.setCosmetic(true);

	QPolygonF polyF;
	polyF << QPointF(0.0002,0.0002)
			<< QPointF(0.0003,0.0002)
			<< QPointF(0.0003,0.0003)
			<< QPointF(0.0002,0.0003);

	QGraphicsPolygonItem* polyItem = new QGraphicsPolygonItem(polyF);

	polyItem->setPen(pen);

	scene.addItem(polyItem);

	ui->graphicsView->setBackgroundBrush(Qt::black);
	ui->graphicsView->setCacheMode(QGraphicsView::CacheBackground);
	ui->graphicsView->setRenderHint(QPainter::Antialiasing);
	ui->graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
	ui->graphicsView->setScene(&scene);

To copy to clipboard, switch view to plain text mode 

if I comment out the following code line it works fine.

ui->graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));

ui->graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));

To copy to clipboard, switch view to plain text mode 

Thanks,
Giuseppe