Inconsistent setFocus and tab sequence behaviors

<?xml version="1.0" encoding="UTF-8"?>
<zk xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
    xmlns='http://www.zkoss.org/2005/zul'
    xmlns:h='http://www.w3.org/1999/xhtml'
    xsi:schemaLocation='http://www.zkoss.org/2005/zul WEB-INF/xsd/zul.xsd'
    anyAttribute= " ">


<window id='testWin' use='GcmScLaunch.ControllerTestWin'
        border='normal' title='A Test Page'>
    
  <!-- This listbox display the movies names  -->
  <listbox id='detailLstBox' width='200px' checkmark='true'>
    <listhead sizable='true'>
      <listheader label='Name'/>
    </listhead>
    <listitem label='Tom And Jerry' value='Tom And Jerry'/>
    <listitem label='Tweety and Sylvester' value='Tweety and Sylvester'/>
    <listitem label='Bugs Bunny' value='Bugs Bunny'/>
  </listbox>
  
  <!-- Edit button to edit the selected row -->
  <space spacing='1px'/>
  <button id='editBtn' label='Edit Record' autodisable='self'
     onClick='testWin.editBtn_onClick()'/>
  
  <!-- ========= Pop-up window to edit selected record ============ -->
        <window id='subEditWin' visible='false' width='500px'
                border='normal' title='Edit Sub-Window' >
          
          <label value='Movie name:'/>
          <textbox id='movieNameTxtBox' width='80%' constraint='no empty'/>

          <separator/>
          <h:center>
            <button id='saveEditBtn' label='Save Record' autodisable='self'
                    onClick='testWin.saveEditBtn_onClick()' />
            
            <button id='closeSubWinBtn' label='Close Window'
                    onClick='testWin.closeSubWinBtn_onClick()'/>
          </h:center>
        </window>
  <!-- ========= End of pop-up Window ============ -->
</window>
</zk>

package GcmScLaunch;

import java.sql.SQLException;
import javax.servlet.ServletContext;
import java.util.*;
import org.zkoss.zul.*;
import org.zkoss.zk.ui.*;
import org.zkoss.zk.ui.event.*;
import org.zkoss.zk.ui.event.EventListener;

/** Controller class for test.zul page */

public class ControllerTestWin extends Window {
  private ZKCommonUtils zkCommonUtils = new ZKCommonUtils();
  /**  Constructor */
  public ControllerTestWin() {
  }//end constructor
  //===========================================================================
  private Listbox getDetailLstBox() throws Exception {
    return (Listbox) getFellow("detailLstBox");  
  }//end method
  private Window getSubWin() throws Exception {
    return (Window) getFellow("subEditWin");
  }//end method
  private Textbox getSubWinTxtBox(Window subWin) throws Exception {
    return (Textbox) subWin.getFellow("movieNameTxtBox");
  }//end method
  private Button getSubWinSaveBtn(Window subWin) throws Exception {
    return (Button) subWin.getFellow("saveEditBtn");
  }//end method
  // ======================Event Handlers======================================        
  /** when you click the Edit Record button */
  public void editBtn_onClick() throws Exception {
    if (this.getDetailLstBox().getSelectedItem() != null) {
      this.getSubWinTxtBox(this.getSubWin()).setValue(
        (String) this.getDetailLstBox().getSelectedItem().getValue()
                                                      );
      this.getSubWinTxtBox(this.getSubWin()).setFocus(true);
      this.getSubWin().doModal();            
    }
    else {
      Messagebox.show("Please select a row first.");
    }
  }//end method
  /** when you click the Save Record button on the Edit Sub-Window */
  public void saveEditBtn_onClick() throws Exception {
    //Some action
  }//end method
  /** when you click the Close Window button on the Edit Sub-Window */
  public void closeSubWinBtn_onClick() throws Exception {
    this.getSubWin().setVisible(false);
  }//end method

}//end class