QGraphicsGridLayout misplaces rightmost widget if its column span is > 1

#include <QtGui>

class Box : public QGraphicsWidget
{
public:
    Box(const QColor &color) : col(color)
    { }
    
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget * = 0)
    {
        painter->fillRect(rect(), col);
    }

protected:
    QSizeF sizeHint(Qt::SizeHint hint, const QSizeF &constraint = QSizeF(-1, -1)) const
    {
        return hint == Qt::PreferredSize
            ? QSizeF(100, 100)
            : QGraphicsWidget::sizeHint(hint, constraint); 
    }

private:
    QColor col;
};

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

    Box *window = new Box(Qt::darkYellow);
    QGraphicsGridLayout *grid = new QGraphicsGridLayout;
    window->setLayout(grid);

    grid->addItem(new Box(Qt::red), 0, 0);
    grid->addItem(new Box(Qt::green), 0, 1);

    // grid->addItem(new Box(Qt::blue), 0, 2);
    grid->addItem(new Box(Qt::blue), 0, 2, 1, 2);

    QGraphicsScene scene;
    scene.addItem(window);

    QGraphicsView view(&scene);
    view.show();

    return app.exec();
}