Application crashes when setWindowFlags() is called with Qt::WindowCancelButtonHint

After setWindowFlags() is called with flag Qt::WindowCancelButtonHint, and close button is clicked. Application crashes.

This behavior is found in Qt 4.4 on Windows vista.

#include <QtGui>

class TMainWindow : public QMainWindow
{
public:
TMainWindow(QWidget* parent = 0)
:
QMainWindow(parent) {}
void mousePressEvent(QMouseEvent*)

{ setWindowFlags(windowFlags() ^ Qt::WindowCancelButtonHint ); qDebug() << windowFlags(); show(); }

};

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

TMainWindow w ;
w.show();
return app.exec();
}