FULL PRODUCT VERSION :
java version "1.6.0-rc"


A DESCRIPTION OF THE PROBLEM :
CardLayout manages its layout stack by setting the top card to visible while the others to invisible. This does not stop the non-visible ones from being layed out. It may be a performance gain to not lay out the non-visible components.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run this test:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class TestCardLayout implements Runnable, ActionListener{

    JFrame jf;
    java.util.Random random = new java.util.Random();
    public void run(){
        final JPanel jp = new JPanel();
        final CardLayout cl = new CardLayout();
        jp.setLayout(cl);
        for(int i = 0; i < 10; i ++)
jp.add(new LayoutPrinter(i), String.valueOf(i));

        jf = new JFrame();
        jf.add(jp);
        jf.setSize(500,500);
        jf.setVisible(true);
        Timer t = new Timer(5000,this);
        t.start();
        JButton jb = new JButton("Random Flip"){
public void fireActionPerformed(ActionEvent e){
                    int i = random.nextInt(10);
                    System.out.println("NEXT CARD IS: " + i);
                    cl.show(jp, String.valueOf(i));
                }
};
        jf.add(jb, BorderLayout.SOUTH);

    }

    boolean add;
    public void actionPerformed(ActionEvent e){
Dimension size = jf.getSize();
        if(add){
           size.width += 1;
           size.height += 1;
           add = false;
}
        else{
size.width -= 1;
            size.height -= 1;
            add = true;
        }
        jf.setSize(size);

    }


    static class LayoutPrinter extends JComponent{
        int n;
        LayoutPrinter(int n){
            this.n = n;
            setLayout(new BorderLayout());
            add(new LayoutPrinter2());
        }
        public void doLayout(){
            getComponent(0).invalidate();
            super.doLayout();
            System.out.println("doLayout for: " + n);
        }

        public class LayoutPrinter2 extends JButton{
            public void doLayout(){
                System.out.println("doLayout2 for: " + n);
           }

}
    }


    public static void main(String ... args){
        SwingUtilities.invokeLater(new TestCardLayout());
    }


}
-----------------
It resizes the frame every 5 seconds, notice how everything is layed out again when it may not be necessary to do this for non-visible components. Press the Random Flip button, notice how the new visible component is layed out as well as the old one. Why does the old one need to be layed out?

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Only the visible "card" component to be layed out
ACTUAL -
everything or one too many components are layed out.

REPRODUCIBILITY :
This bug can be reproduced always.

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

public class TestCardLayout implements Runnable, ActionListener{

    JFrame jf;
    java.util.Random random = new java.util.Random();
    public void run(){
        final JPanel jp = new JPanel();
        final CardLayout cl = new CardLayout();
        jp.setLayout(cl);
        for(int i = 0; i < 10; i ++)
jp.add(new LayoutPrinter(i), String.valueOf(i));

        jf = new JFrame();
        jf.add(jp);
        jf.setSize(500,500);
        jf.setVisible(true);
        Timer t = new Timer(5000,this);
        t.start();
        JButton jb = new JButton("Random Flip"){
public void fireActionPerformed(ActionEvent e){
                    int i = random.nextInt(10);
                    System.out.println("NEXT CARD IS: " + i);
                    cl.show(jp, String.valueOf(i));
                }
};
        jf.add(jb, BorderLayout.SOUTH);

    }

    boolean add;
    public void actionPerformed(ActionEvent e){
Dimension size = jf.getSize();
        if(add){
           size.width += 1;
           size.height += 1;
           add = false;
}
        else{
size.width -= 1;
            size.height -= 1;
            add = true;
        }
        jf.setSize(size);

    }


    static class LayoutPrinter extends JComponent{
        int n;
        LayoutPrinter(int n){
            this.n = n;
            setLayout(new BorderLayout());
            add(new LayoutPrinter2());
        }
        public void doLayout(){
            getComponent(0).invalidate();
            super.doLayout();
            System.out.println("doLayout for: " + n);
        }

        public class LayoutPrinter2 extends JButton{
            public void doLayout(){
                System.out.println("doLayout2 for: " + n);
           }

}
    }


    public static void main(String ... args){
        SwingUtilities.invokeLater(new TestCardLayout());
    }


}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Uncertain, as laying out appears to rely upon an internal field to determine if it should layout children.