FULL PRODUCT VERSION :
java version "1.6.0_10"
Java(TM) SE Runtime Environment (build 1.6.0_10-b33)
Java HotSpot(TM) Client VM (build 11.0-b15, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
When using the XP style look and feel on Windows XP, a JPanel added to a JInternalFrame becomes higher than the set preferred size.

Occurs for Java 1.4.2, 1.5 and 1.6.x

When running with -Dswing.noxp=true, the panel size is correct

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the attached example

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Expected the panel size after pack() to be the preferred size
ACTUAL -
The panel in the JInternalFrame is 4 pixels too high

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.*;
import javax.swing.*;

public class SizeTest
{
   public static void main( String[] args )
   {
      try
      {
         UIManager.setLookAndFeel( UIManager.getSystemLookAndFeelClassName() );
      }
      catch ( Exception e )
      {
         e.printStackTrace();
      }

      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
      JDesktopPane dp = new JDesktopPane();
      frame.getContentPane().add( dp );
      frame.setSize( 800, 600 );
      frame.setVisible( true );

      JInternalFrame iFrame = new JInternalFrame();
      JPanel p = new JPanel();
      p.setPreferredSize( new Dimension( 500, 400 ) );
      iFrame.getContentPane().add( p );
      iFrame.pack();
      iFrame.setVisible( true );

      dp.add( iFrame );
      System.out.println( p.getBounds() );
   }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Decrease the internal frame height by 4 pixels after pack
or use -Dswing.noxp=true