<Swing Dev> redefenition isValid() method from Component

[sablintolya at gmail.com]

import javax.swing.WindowConstants;

public class Main {

  public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {

      public void run() {
        final JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.add(new NewPanel());
        frame.setPreferredSize(new Dimension(400, 300));
        frame.pack();
        frame.setVisible(true);
      }
    });
  }
}

class NewPanel extends JPanel {

  public NewPanel() {
    add(new JLabel("Test"));
  }

  @Override
  public boolean isValid() {
    return true;
  }
}

And if I run this code under openjdk it shows panel with label, but if I run 
this code under propriertary sunjdk it shows panel without label.

If comment isValid() method, it works equally.

Why such a difference and who is working correctly?

sun jdk:
$ java -version
java version "1.6.0_22"
Java(TM) SE Runtime Environment (build 1.6.0_22-b04)
Java HotSpot(TM) 64-Bit Server VM (build 17.1-b03, mixed mode)

openjdk:
$ java -version
java version "1.6.0_18"
OpenJDK Runtime Environment (IcedTea6 1.8.3) (6b18-1.8.3-2)
OpenJDK 64-Bit Server VM (build 16.0-b13, mixed mode)

my system:
$ uname -a
Linux sablin 2.6.32-5-amd64 #1 SMP Fri Dec 10 15:35:08 UTC 2010 x86_64 
GNU/Linux

$ lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 5.0.7 (lenny)
Release:        5.0.7
Codename:       lenny

$ cat /etc/debian_version 
squeeze/sid

With regards, Anatoliy