Painting artefacts when using QPen with style other than SolidLine in QGraphicsView

[Radagast]

Qt 4.6.0 (SDK for Windows with MinGW)
Hello!
Here is the minimum example:
mainwindow.cpp :

#include <QGraphicsView>
#include "mainwindow.h"
#include "myscene.h"
 
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
	MyScene* s = new MyScene(this);
	s->setSceneRect(-1000,-1000,3000,3000);
	QGraphicsView* v = new QGraphicsView(s);
	setCentralWidget(v);
}

#include <QGraphicsView>
#include "mainwindow.h"
#include "myscene.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
	MyScene* s = new MyScene(this);
	s->setSceneRect(-1000,-1000,3000,3000);
	QGraphicsView* v = new QGraphicsView(s);
	setCentralWidget(v);
}

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myscene.cpp:

#include <QGraphicsEllipseItem>
#include <QGraphicsSceneMouseEvent>
#include "myscene.h"
 
MyScene::MyScene(QObject *parent) :
    QGraphicsScene(parent)
{
}
void MyScene::mouseDoubleClickEvent ( QGraphicsSceneMouseEvent * e )
{
	QRectF circleRect(0,0,600,600);
	circleRect.moveCenter(e->scenePos());
	QGraphicsEllipseItem* el = new QGraphicsEllipseItem(circleRect);
	el->setPen(QPen(Qt::red, 4, Qt::DashLine));
	addItem(el);
}

#include <QGraphicsEllipseItem>
#include <QGraphicsSceneMouseEvent>
#include "myscene.h"

MyScene::MyScene(QObject *parent) :
    QGraphicsScene(parent)
{
}
void MyScene::mouseDoubleClickEvent ( QGraphicsSceneMouseEvent * e )
{
	QRectF circleRect(0,0,600,600);
	circleRect.moveCenter(e->scenePos());
	QGraphicsEllipseItem* el = new QGraphicsEllipseItem(circleRect);
	el->setPen(QPen(Qt::red, 4, Qt::DashLine));
	addItem(el);
}

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main.cpp, myscene.h and mainwindow.h are the default as generated by QtCreator (except that I added mouseDoubleClickEvent declaration to myscene.h).
When I double click in the corner of the view, the ellipse appears (Only part of it fits in the view and that's OK), and when I scroll the view to the right, I see this:

If I use Qt::SolidLine, everything is fine, but with Qt:ashLine and all other styles I see this painting artefact.
Thanks in advance.