In QMdiSubWindow heightForWidth() does not work.

#include <QApplication>
#include <QWidget>
#include <QDebug>
#include <QVBoxLayout>
#include <QMdiArea>
#include <QMainWindow>
#include <QMdiSubWindow>


class OwnSubWindow : public QMdiSubWindow {
    mutable int m_ctr;
public:
    OwnSubWindow(QWidget *parent = 0) : QMdiSubWindow(parent), m_ctr(0) {
        QSizePolicy p(sizePolicy());
        p.setHeightForWidth(true);
        setSizePolicy(p);
    }
    int heightForWidth(int width) const {
        qDebug()<<"heightforwidth "<<m_ctr;
        m_ctr ++;
        qApp->postEvent(const_cast<OwnSubWindow*>(this), new QEvent(QEvent::UpdateRequest));
        return qMax(width*2, 100);
    }
    QSize sizeHint() const {
        return QSize(300, heightForWidth(300));
    }
};

class Widget : public QWidget {
    mutable int m_ctr;
public:
    Widget(QWidget *parent = 0) : QWidget(parent), m_ctr(0) {
        QSizePolicy p(sizePolicy());
        p.setHeightForWidth(true);
        setSizePolicy(p);
    }
    int heightForWidth(int width) const {
        qDebug()<<"heightforwidth "<<m_ctr;
        m_ctr ++;
        QApplication::postEvent(const_cast<Widget*>(this), new QEvent(QEvent::UpdateRequest));
        return qMax(width*2, 100);
    }
    QSize sizeHint() const {
        return QSize(300, heightForWidth(300));
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QMainWindow w1;
    QMdiArea *mdiArea = new QMdiArea();

    mdiArea->addSubWindow(new OwnSubWindow);
    mdiArea->addSubWindow(new Widget);

    w1.setCentralWidget(mdiArea);
    w1.show();

    QWidget w;
    QVBoxLayout * l = new QVBoxLayout(&w);
    l->addWidget(new Widget);
    w.show();
    return a.exec();
}