Reparenting widgets to different screens on X11

Reparenting widgets to a different display doesn't seem to work very well on X11.

To reproduce:

run this example on X11 on a computer with multiple DISPLAY's (e.g. 0.0, 0.1 etc).
click the radio button to switch screen for a window. Note that the subwidgets don't paint on the new screen (though you can still click on them)

#include <QtGui>

class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(int screen)
: QMainWindow(qApp->desktop()->screen(screen))
{
setCentralWidget(new QWidget(this));
QVBoxLayout *lay = new QVBoxLayout(centralWidget());
for (int i=0; i<qApp->desktop()->numScreens(); ++i)

{ QRadioButton *rb = new QRadioButton(QString("Screen %1").arg(i), centralWidget()); lay->addWidget(rb); buttons.append(rb); }

buttons.at(screen)->setChecked(true);
foreach(QRadioButton *rb, buttons)

{ connect(rb, SIGNAL(toggled(bool)), this, SLOT(changeScreen(bool))); }

setAttribute(Qt::WA_DeleteOnClose);
}
public slots:
void changeScreen(bool toggled)

{ if (!toggled) return; int s = buttons.indexOf(qobject_cast<QRadioButton*>(sender())); setParent(qApp->desktop()->screen(s)); show(); }

private:
QList<QRadioButton*> buttons;
};

#include "main.moc"

int main(int argc, char **argv)
{
QApplication a(argc, argv);
QList<MainWindow*> windows;
for (int i=0; i<a.desktop()->numScreens(); ++i)

{ MainWindow *mw = new MainWindow(i); windows.append(mw); mw->show(); }

return a.exec();
}