QGraphicsPolygonItem is not drawn with the right pen attributes when it covers a large area

QGraphicsPolygonItem is not drawn with the right pen attributes when it covers a large area. It is not showing the pen as a dash line when it is set to use one, but this can vary depending on the size of the line. If it is smaller then it can show up fine. Using the same polygon via a QPainter onto a QPixmap works fine too.