Double buffering issue

Question

I have a complex modal JDialog with many JTextFields. Before it becomes visible I call setText("") on these fields to reset their values. When the dialog appears for the second time I see for a moment the old values of these fields. There is no such behaviour if I turn off double buffering on JRootPane of this dialog. Is it a bug or by design? It looks very ugly.
JDK 1.6.0.27, Linux 2.6.31

Answer 1

Here is an example. Click 'open', click 'fill values', close the dialog. Repeat until you see the old values in the JTextFields for a blink of an eye. Uncomment XXX to avoid this effect.
public class Test
    private static MyDialog dialog;
    public Test()
    public static void main(String[] args) throws Exception
        SwingUtilities.invokeLater(new Runnable()
            @Override
            public void run()
                final JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new FlowLayout());
                JButton b = new JButton(new AbstractAction("Open")
                    @Override
                    public void actionPerformed(ActionEvent e)
                        if (dialog == null)
                            dialog = new MyDialog(frame);
                            dialog.pack();
                            dialog.setLocationRelativeTo(frame);
                            dialog.setModal(true);
                        dialog.clear();
                        dialog.setVisible(true);
                frame.add(b);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
    private static class MyDialog extends JDialog
        private JTextField[] textFields;
        public MyDialog(Frame owner)
            super(owner);
            // XXX
            //getRootPane().setDoubleBuffered(false);
            int n = 20;
            setLayout(new GridLayout(n + 1, 2));
            textFields = new JTextField[n];
            for (int i = 0; i < n; ++i)
                JTextField tf = new JTextField();
                tf.setColumns(10);
                textFields[i] = tf;
                add(new JLabel("Field " + i));
                add(tf);
            JButton b = new JButton(new AbstractAction("Fill values")
                @Override
                public void actionPerformed(ActionEvent e)
                    Random rnd = new Random();
                    for (JTextField tf : textFields)
                        tf.setText(Integer.toString(rnd.nextInt()));
            add(b);
        private void clear()
            for (JTextField tf : textFields)
                tf.setText("");
}