setScrollPosition(int position) blackberry

Question

Hi all!

Here is the cod:

public class MyTextField extends MainScreen{

private RichTextField textField;

private VerticalFieldManager manager;

public MyTextField();

initUi();

 }

   public void initUi(){
        manager = new VerticalFieldManager(VerticalFieldManager.VERTICAL_SCROLL |
                                           VerticalFieldManager.VERTICAL_SCROLLBAR);
        String text = "text here can be very long - more than ten screens to scroll 
                        with default font size";
        textField = RichTextField(text, Field.NON_FOCUSABLE); 
        manager.add(textField);
        add(manager);
   }
   protected void onDisplay(){
        Dialog.alert("Loaded");
        textField.getManager().setScrollPosition(3000);
   }

so it does set position in this way, but if I comment Dialog.alert("Loaded"); it sets scroll position only on two screens it's 600px about, Please can anyone tell me what should I do to get it work?

Thanks in advance!!!