FULL PRODUCT VERSION :
Executed in Eclipse under JRE 1.4.2_11

The java -version output is:
java version "1.5.0_06"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_06-b05)
Java HotSpot(TM) Client VM (build 1.5.0_06-b05, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Windows XP Professional (Service Pack 2)

A DESCRIPTION OF THE PROBLEM :
The application contains a JTextpane that formats keywords after typing and undoing or redoing. Undo and redo are invoked by ctrl-z and ctrl-y. It woks fine for all but not in one case: Enter a newline character somewhere in the text and undo this afterwards. The document is destroyed. The rest after the undo location is visually gone.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Execute the application and enter a newline char somewhere. Best would be to go the word "else" and press enter in the middle of it.
Press ctrl-z afterwards.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The entered newline char should just be removed by the undo in order to restore the old contents.
ACTUAL -
The document is destroyed. The rest after the undo location is visually gone. If you debug you`ll find out that the text is still in the document but viusally the rest after the undo location is gone and the focus is lost. Hitting any of the keys <- or -> will cause an ArrayIndexOutOfBoundsException.

ERROR MESSAGES/STACK TRACES THAT OCCUR :
One of the consequences of loss of focus is:

java.lang.ArrayIndexOutOfBoundsException: -1
at javax.swing.text.CompositeView.getView(CompositeView.java:143)
at javax.swing.text.Utilities.getNextVisualPositionFrom(Utilities.java:763)
at javax.swing.text.CompositeView.getNextEastWestVisualPositionFrom(CompositeView.java:731)
at javax.swing.text.CompositeView.getNextVisualPositionFrom(CompositeView.java:457)
at javax.swing.plaf.basic.BasicTextUI$RootView.getNextVisualPositionFrom(BasicTextUI.java:1465)
at javax.swing.plaf.basic.BasicTextUI.getNextVisualPositionFrom(BasicTextUI.java:1028)
at javax.swing.text.DefaultEditorKit$NextVisualPositionAction.actionPerformed(DefaultEditorKit.java:1560)
at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1530)
at javax.swing.JComponent.processKeyBinding(JComponent.java:2438)
at javax.swing.JComponent.processKeyBindings(JComponent.java:2473)
at javax.swing.JComponent.processKeyEvent(JComponent.java:2401)
at java.awt.Component.processEvent(Component.java:4909)
at java.awt.Container.processEvent(Container.java:1569)
at java.awt.Component.dispatchEventImpl(Component.java:3615)
at java.awt.Container.dispatchEventImpl(Container.java:1627)
at java.awt.Component.dispatchEvent(Component.java:3477)
at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1713)
at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:627)
at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:831)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:741)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:592)
at java.awt.Component.dispatchEventImpl(Component.java:3506)
at java.awt.Container.dispatchEventImpl(Container.java:1627)
at java.awt.Window.dispatchEventImpl(Window.java:1606)
at java.awt.Component.dispatchEvent(Component.java:3477)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:480)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:145)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:137)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:100)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
package de.rge.fileeditor;

import java.awt.event.ActionEvent;

import javax.swing.AbstractAction;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.KeyStroke;
import javax.swing.event.UndoableEditEvent;
import javax.swing.event.UndoableEditListener;
import javax.swing.text.AbstractDocument;
import javax.swing.text.BadLocationException;
import javax.swing.undo.CannotRedoException;
import javax.swing.undo.CannotUndoException;
import javax.swing.undo.UndoManager;


public class EditorWin extends JFrame{
private JScrollPane spEditor = null;
private JTextPane textPane = null;
private UndoManager undomanager = new UndoManager();
private EditorDocument document = null;

public static void main(String[] args) {
EditorWin win = new EditorWin();
win.initialize();
}

public EditorWin(){
initialize();
setVisible(true);
}


private void initialize() {
try {
setSize(500, 300);
getContentPane().add(getspEditor(), getspEditor().getName());
} catch (java.lang.Throwable ivjExc) {
}
    }

/**
* This method initializes spEditor
*
* @return javax.swing.JScrollPane
*/
private JScrollPane getspEditor() {
if(spEditor == null) {
spEditor = new JScrollPane(getTextPane());
spEditor.setBounds(10, 10, getWidth() -20, getHeight()-100);
}
return spEditor;
}

public JTextPane getTextPane(){
if(textPane == null) {
document = new EditorDocument();
textPane = new JTextPane(document);

openText();

// Listen for undo and redo events (but ignore format changes)
document.addUndoableEditListener(new UndoableEditListener() {
public void undoableEditHappened(UndoableEditEvent evt) {
String action = ((AbstractDocument.DefaultDocumentEvent)evt.getEdit()).getType().toString();
if(action.equals("CHANGE")){
return; // Ignore any format events
}else{
undomanager.addEdit(evt.getEdit());
}
}
});

// Create an undo action and add it to the text component
textPane.getActionMap().put("Undo",
new AbstractAction("Undo") {
public void actionPerformed(ActionEvent evt) {
try {
if (undomanager.canUndo()) {
undomanager.undo();
}
} catch (CannotUndoException e) {
System.out.println("CannotUndoException");
}
}
});

// Bind the undo action to ctl-Z
textPane.getInputMap().put(KeyStroke.getKeyStroke("control Z"), "Undo");

// Create a redo action and add it to the text component
textPane.getActionMap().put("Redo",
new AbstractAction("Redo") {
public void actionPerformed(ActionEvent evt) {
try {
if (undomanager.canRedo()) {
undomanager.redo();
}
} catch (CannotRedoException e) {
System.out.println("CannotRedoException");
}
}
});

// Bind the redo action to ctl-Y
textPane.getInputMap().put(KeyStroke.getKeyStroke("control Y"), "Redo");
document.format();
}
return textPane;
}

public void openText(){
try{
String text ="Go to the middle of else and press enter and ctrl-z afterwards";
textPane.getDocument().insertString(0, text, null);
}
catch(BadLocationException ble){
System.out.println("Error in openText");
}
}
}




package de.rge.fileeditor;

import java.awt.Color;
import java.awt.Font;
import java.util.StringTokenizer;

import javax.swing.event.DocumentEvent;
import javax.swing.text.BadLocationException;
import javax.swing.text.DefaultStyledDocument;
import javax.swing.text.Style;
import javax.swing.text.StyleConstants;

public class EditorDocument extends DefaultStyledDocument
{
private Style myStyle1 = null;
private Style myStyle2 = null;
private Style myStyle3 = null;
private Font myFont = new Font("Monospaced", Font.PLAIN, 1);

public EditorDocument(){
myStyle1 = addStyle("myStyle1", getStyle("default"));
StyleConstants.setFontSize(myStyle1, 15);
StyleConstants.setFontFamily(myStyle1, myFont.getName());
StyleConstants.setItalic(myStyle1, false);
StyleConstants.setBold(myStyle1, true);
StyleConstants.setForeground(myStyle1,Color.BLUE);
StyleConstants.setBackground(myStyle1,Color.WHITE);
StyleConstants.setUnderline(myStyle1, false);

Font myFont2 = new Font("Monospaced", Font.PLAIN, 12);
myStyle2 = addStyle("myStyle2", getStyle("default"));
StyleConstants.setFontSize(myStyle2, 15);
StyleConstants.setFontFamily(myStyle2, myFont2.getName());
StyleConstants.setItalic(myStyle2, false);
StyleConstants.setBold(myStyle2, true);
StyleConstants.setForeground(myStyle2,Color.GREEN);
StyleConstants.setBackground(myStyle2,Color.WHITE);
StyleConstants.setUnderline(myStyle2, false);

Font myFont3 = new Font("Monospaced", Font.PLAIN, 12);
myStyle3 = addStyle("myStyle3", getStyle("default"));
StyleConstants.setFontSize(myStyle3, 15);
StyleConstants.setFontFamily(myStyle3, myFont3.getName());
StyleConstants.setItalic(myStyle3, false);
StyleConstants.setBold(myStyle3, true);
StyleConstants.setForeground(myStyle3,Color.BLACK);
StyleConstants.setBackground(myStyle3,Color.WHITE);
StyleConstants.setUnderline(myStyle3, false);
}

protected void fireInsertUpdate(DocumentEvent e)
{
        super.fireInsertUpdate(e);
        format();
}

protected void fireRemoveUpdate(DocumentEvent e)
{
        super.fireRemoveUpdate(e);
        format();
}

public void format()
{
try{
String text = getText(0,getLength());
StringTokenizer wordTokenizer = new StringTokenizer(text);
int anzahlToken = wordTokenizer.countTokens();
int tokenStart = 0;
for(int w=0; w < anzahlToken; w++)
{
String word = wordTokenizer.nextToken();
tokenStart = text.indexOf(word,tokenStart);
// System.out.println("Word = '" + word + "' at Pos: " + tokenStart);
applyFormatToWord(word,tokenStart);
tokenStart = tokenStart+ word.length();
}
}catch(BadLocationException ble){}
}

private void applyFormatToWord( String word, int wordStart )
{
if(word.equals("to")){
setCharacterAttributes(wordStart,
word.length(),
myStyle1,
true);
}
else if(word.equals("the")){
setCharacterAttributes(wordStart,
word.length(),
myStyle1,
true);
}
else if(word.equals("else")){
setCharacterAttributes(wordStart,
word.length(),
myStyle1,
true);
}
else if(word.equals("press")){
setCharacterAttributes(wordStart,
word.length(),
myStyle1,
true);
}
else if(word.equals("enter")){
setCharacterAttributes(wordStart,
word.length(),
myStyle2,
true);
}
else{
setCharacterAttributes(wordStart,
word.length(),
myStyle3,
true);
}
}
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
None found so far