Setting flags on QMdiSubWindow in the QMdiArea doesn't work correctly

#include <QtGui>

class ControlWidget : public QMdiArea
{
    Q_OBJECT

public:
    ControlWidget(QWidget *parent = 0) : QMdiArea(parent)
    {
        QPushButton *pb = new QPushButton("Swap flags");
        addSubWindow(pb);
        swFrameless = addSubWindow(new QTextEdit, Qt::FramelessWindowHint);
        swWithFrame = addSubWindow(new QTextEdit);

        originalWindowFlags = swWithFrame->windowFlags();

        swap = true;

        connect(pb, SIGNAL(clicked()), this, SLOT(swapFlags()));
    }

public slots:
    void swapFlags()
    {
        if (swap)
        {
            QRect geo1 = swWithFrame->geometry();
            swWithFrame->setWindowFlags(Qt::FramelessWindowHint);
            swWithFrame->setParent(0);
            addSubWindow(swWithFrame);
            swWithFrame->setGeometry(geo1);

            QRect geo2 = swFrameless->geometry();
            swFrameless->setWindowFlags(originalWindowFlags);
            swFrameless->setParent(0);
            addSubWindow(swFrameless);
            swFrameless->setGeometry(geo2);
        }
        else
        {
            QRect geo1 = swWithFrame->geometry();
            swWithFrame->setWindowFlags(originalWindowFlags);
            swWithFrame->setParent(0);
            addSubWindow(swWithFrame);
            swWithFrame->setGeometry(geo1);

            QRect geo2 = swFrameless->geometry();
            swFrameless->setWindowFlags(Qt::FramelessWindowHint);
            swFrameless->setParent(0);
            addSubWindow(swFrameless);
            swFrameless->setGeometry(geo2);
        }

        swWithFrame->show();
        swFrameless->show();

        swap = !swap;
    }

private:
    QMdiSubWindow *swFrameless;
    QMdiSubWindow *swWithFrame;
    Qt::WindowFlags originalWindowFlags;
    bool swap;
};

#include "main.moc"

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

    ControlWidget area;
    area.show();

    return app.exec();
}