Transparent JDesktopPane

I was so very happy today, because I had my UI looking just really blody
flash. Then I tried moving a JInternalFrame, and the whole house of
cards tumbled down.

My whole L&F depends on having a JPanel in the background of an MDI
form. That background panel has a tiled image of a cute little
watermark. Buttons on the left, JDesktop taking up the rest of the
space, with JInternal frames popping up as required.

As I said in my opening paragraph, the problem is that moving the
JInternalFrames about leaves a mess behind on the JDesktopPane.

I've put together a simple class that shows my problem exactly. It'll
wrap, but it's also available for download at...

http://www.webber.com.au/pub/TransparentMDI.java

I'd greatly appreciate any thought on this. The sample code is below.

TIA,
Luke

------------------------------------------------------------
package test;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

/*
  * A sample of problems encountered with transparent JDesktopPanes
  *
  * If pnlLeft isn't added, the red background from pnlMain doesn't
  * even show though, but that's not the biggest problem.
  * Moving the JInternalFrame around (WinXP, JDK1.5.0_07), makes one
  * hell of a mess. OTOH, resizing the internal frame works just fine,
  * even removing the artifacts left by previous moves.
  */
public class TransparentMDI extends JFrame implements WindowListener
{
   JDesktopPane desktop = new JDesktopPane();

   public static void main(String[] args)
   {
     new TransparentMDI().setVisible(true);
   }

   public TransparentMDI()
   {
     super("Transparent Desktop Test");
     Container cp = getContentPane();
     JPanel pnlMain = new JPanel(new BorderLayout());
     pnlMain.setBackground(Color.RED);
     JPanel pnlLeft = new JPanel(new BorderLayout());
     pnlLeft.setOpaque(false);
     pnlLeft.add(new JLabel("JDK "+System.getProperty("java.version")),
BorderLayout.NORTH);
     pnlMain.add(pnlLeft, BorderLayout.WEST);
     // Make the desktop semi-transparent
     Color db = new Color(0,0,0, 32);
     desktop.setBackground(db);
     desktop.setOpaque(false);
     pnlMain.add(desktop, BorderLayout.CENTER);
     JInternalFrame jif = new JInternalFrame("Internal Frame", true, true);
     jif.setBounds(0, 0, 300, 300);
     Container jifcp = jif.getContentPane();
     jifcp.setLayout(new BorderLayout());
     jifcp.add(new JLabel("Move me", JLabel.CENTER), BorderLayout.CENTER);
     jif.setVisible(true);
     desktop.add(jif);
     cp.setLayout(new BorderLayout());
     cp.add(pnlMain, BorderLayout.CENTER);
     addWindowListener(this);
     pack();
     setExtendedState(MAXIMIZED_BOTH);
   }

   public void windowClosing(WindowEvent we)
   {
     System.exit(0);
   }

   public void windowActivated(WindowEvent e) {}
   public void windowClosed(WindowEvent e) {}
   public void windowDeactivated(WindowEvent e) {}
   public void windowDeiconified(WindowEvent e) {}
   public void windowIconified(WindowEvent e) {}
   public void windowOpened(WindowEvent e) {}
}
----------------------------------------------------------