FULL PRODUCT VERSION :
java version "1.6.0"
Java(TM) SE Runtime Environment (build 1.6.0-b105)
Java HotSpot(TM) Client VM (build 1.6.0-b105, mixed mode, sharing)

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

EXTRA RELEVANT SYSTEM CONFIGURATION :
The problem also happens under JRE 1.5.0

A DESCRIPTION OF THE PROBLEM :
Serializing a frame that contains a JComboBox with a custom editor leads an exception (see the Error Messages field). It appears that the UI delegate is being uninstalled during serialization and not reinstalled. This may be related to bug 5081305.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the attached Java program
In the UI that appears click the "Serialize" button
Observe the exception

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No exception
ACTUAL -
Exception

ERROR MESSAGES/STACK TRACES THAT OCCUR :
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at javax.swing.plaf.basic.BasicComboBoxUI.paint(BasicComboBoxUI.java:846)
        at javax.swing.plaf.ComponentUI.update(ComponentUI.java:142)
        at javax.swing.JComponent.paintComponent(JComponent.java:742)
        at javax.swing.JComponent.paint(JComponent.java:1005)
        at javax.swing.JComponent.paintWithOffscreenBuffer(JComponent.java:4963)
        at javax.swing.JComponent.paintDoubleBuffered(JComponent.java:4916)
        at javax.swing.JComponent._paintImmediately(JComponent.java:4859)
        at javax.swing.JComponent.paintImmediately(JComponent.java:4666)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:451)
        at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.
java:114)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:461)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:242)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:163)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:157)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:149)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)


REPRODUCIBILITY :
This bug can be reproduced always.

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

public class SerializationProblem
{
    public static void main(String[] args) {

        try {UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());}
        catch (Exception e) {}

        final JFrame frame = new JFrame("Serialization Problem");
        JComboBox comboBox = new JComboBox(new Object[] {"Item 1", "Item 2", "Item 3"});
        JButton button = new JButton("Serialize");

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        comboBox.setEditor(new CustomEditor());

        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                try {
                    FileOutputStream fileOut = new FileOutputStream("temp.dat");
                    ObjectOutputStream objectOut = new ObjectOutputStream(fileOut);
                    objectOut.writeObject(frame);
                    objectOut.close();
                    fileOut.close();
                } catch (IOException ioe) {}
            }
        });

        frame.getContentPane().add(comboBox, BorderLayout.NORTH);
        frame.getContentPane().add(button, BorderLayout.SOUTH);

        frame.pack();
        frame.setVisible(true);
    }

    static class CustomEditor extends BasicComboBoxEditor //.UIResource // Uncommenting this prevents the problem
    {
        CustomEditor() {editor = new JTextField(15);}
    }
}

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

CUSTOMER SUBMITTED WORKAROUND :
Tagging the custom editor as a UIResource prevents the problem but this isn't always desirable.