QImage drawEllipse bug

#include <QtGui>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QImage im(500, 500, QImage::Format_ARGB32_Premultiplied);
    im.fill(QColor(Qt::blue).rgba());
    QPainter p(&im);
    QPen pen1;
    pen1.setStyle(Qt::DashLine);
    pen1.setColor(Qt::white);
    pen1.setCapStyle(Qt::FlatCap);
    QPen pen2;
    pen2.setStyle(Qt::SolidLine);
    pen2.setColor(Qt::red);
    QPen *pens[] = { &pen1, &pen2, 0 };
    for (int i=0; pens[i]; ++i) {
        pens[i]->setWidthF(150);
        p.setPen(*pens[i]);
        p.drawEllipse(100, 100, 300, 300);
    }
    QLabel lbl;
    lbl.setPixmap(QPixmap::fromImage(im));
    lbl.show();
    return app.exec();
}