QPolygon::containsPoint different results when point on boundary

// make square polygon
QPolygon polygon;
polygon <<
   QPoint(10, 10)   << QPoint(-10, 10) <<
   QPoint(-10, -10) << QPoint(10, -10);

// both points on the edges
QPoint right = QPoint(10, 0);
QPoint left  = QPoint(-10, 0);

// dfferent results
Q_ASSERT(
    polygon.containsPoint(right, Qt::OddEvenFill) ==
    polygon.containsPoint(left, Qt::OddEvenFill)
);