Undo problem in DefaultStyledDocument!

Question

Just run this code, and you won't be able to type in the editor pane! What's the problem? Indeed the problem arose from the setCharacterAttributes(), and rejection of change events in the overriden implementation of undoableEditHappened from UndoManager. How can this be fixed? Please don't say I'm supposed to save all these change events and undo them as well.
import javax.swing.*;
import javax.swing.text.*;
import javax.swing.event.*;
import javax.swing.undo.UndoManager;
public class pad {
    public static void main(String[] arguments) throws BadLocationException {
      JFrame pad = new JFrame();
      pad.setBounds(50, 50, 400, 300);
      pad.setVisible(true);
      JEditorPane editor = new JEditorPane();
      pad.getContentPane().add(editor);
      editor.setEditorKit(new StyledEditorKit());
      DefaultStyledDocument document = (DefaultStyledDocument) editor.getDocument();
      UndoManager undoManager = new UndoManager() {
       public void undoableEditHappened(UndoableEditEvent e) {
           // The problem arose from the rejection of change event here!
           if (((DocumentEvent) e.getEdit()).getType() == DocumentEvent.EventType.CHANGE)
            return;
           super.undoableEditHappened(e);
      document.addUndoableEditListener(undoManager);
      editor.replaceSelection("n\n");
      document.setCharacterAttributes(0, 1, SimpleAttributeSet.EMPTY, false);
      undoManager.undo();
}

Answer 1

Of course if you replace "n\n" with "1" or any string not ending with '\n', it works fine! The "n\n" is a typical input which causes the malfunctioning of the UndoManager, and which the user may type! All I do is highlighting the input. Then the user tries to undo the last typed entries 'n', & '\n'! I've rejected the highlighting change events so that I can undo the user's input at each undo.
That's it! I didn't do anything wrong except not considering the change events!
Anyway, thanks for your attention camickr!
Regards,
--Rasta