Unexpected result when drawing a dotted line

#include <QtOpenGL>

int main(int argc, char *argv[])
{
	QApplication app(argc, argv);

	QGraphicsScene scene(0, 0, 700, 500);
	QGraphicsView view;
	view.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing);

	// BLOCK 1
	{
		QGLWidget *widget = new QGLWidget(QGLFormat(QGL::SampleBuffers));
		view.setViewport(widget);
	}

	view.setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
	view.setScene(&scene);
	view.resize(800, 600);
	view.show();

	QGraphicsRectItem *unitRect = new QGraphicsRectItem(0, 0, 1, 1);
	unitRect->setScale(400);
	scene.addItem(unitRect);

	QPen dotPen(Qt::red, 0, Qt::DotLine);

	// BLOCK 2
	{
		QGraphicsLineItem *line1 = new QGraphicsLineItem(0.1, 0.1, 0.1, 0.5, unitRect);
		line1->setPen(dotPen);

		QGraphicsLineItem *line2 = new QGraphicsLineItem(-5, -5, 10, 10, line1);
		line2->setPos(line1->line().p1());
		line2->setFlag(QGraphicsItem::ItemIgnoresTransformations);
		line2->setPen(QPen(Qt::black));
	}

	// BLOCK 3
	{
		QGraphicsLineItem *line3 = new QGraphicsLineItem(0.9, 0.1, 0.9, 0.1, unitRect);
		line3->setPen(dotPen);
	}

	return app.exec();
}