Listbox focus problem after item's deletion via ctrl key

<window id="testWindow" 
        title="Test Window" 
        border="normal"
        width="50%"
        height="50%"
        sizable="true" 
        closable="true"
        mode="overlapped"
        maximizable="true"
        minimizable="true">
 
  <button label="Add" onClick="add()" />
  <button label="Delete" onClick="delete()" />
  
  <separator bar="true" />
  
  <zscript>
    <![CDATA[
	  // data init
	  List data = new ArrayList();
	  for(int i; i < 21; i++) {
    	data.add("Option" + i); 
    }

	  ListModel modelList = new ListModelList(data);
	  
  	// listbox's listeners
	  void addListboxListeners() {
	   // ctrl keys listener
  		testListbox.addEventListener(Events.ON_CTRL_KEY, new org.zkoss.zk.ui.event.EventListener() {
	  		public void onEvent(Event event) throws Exception {
		  	  switch (((KeyEvent) event).getKeyCode()) {
		        case KeyEvent.INSERT : add(); break;
		        case KeyEvent.DELETE : delete(); break;
		      }
			  }
		  });
	  }

	  // add new option
	  void add() {
	  	int selectedIndex = testListbox.getSelectedIndex();
      if (selectedIndex != -1) {
        ((ListModelList) testListbox.getModel()).add(selectedIndex, "Added option");
        testListbox.setSelectedIndex(selectedIndex);
        testListbox.focus();
      }
      else {
      	alert("No selected item.");
      }
	  }
	  
	  // delete selected option
	  void delete() {
      int selectedIndex = testListbox.getSelectedIndex();
      if (selectedIndex != -1) {
        ((ListModelList) testListbox.getModel()).remove(selectedIndex);
  			if (selectedIndex == 0) {
  				if (testListbox.getItems().size() != 0) {
  					testListbox.setSelectedIndex(0);
  				}
  			}
  			else {
  				testListbox.setSelectedIndex(selectedIndex - 1);
  			}
        testListbox.focus();
      }
      else {
      	alert("No selected item.");
      }
	  }
    ]]>
  </zscript>

  <listbox id="testListbox" 
           model="${modelList}" 
           rows="10" 
           ctrlKeys="#ins#del" 
           onCreate="addListboxListeners()" />

</window>