BlackBerry - MainScreen with labels vertical scroll

I am trying to create a MainScreen with vertical scrolling. From what I've read in the documentation, MainScreen has a VerticalManager inside, so it should be possible to enable vertical scrolling only with proper construction, i.e:

super(MainScreen.VERTICAL_SCROLL | MainScreen.VERTICAL_SCROLLBAR);

This is not working for me, however. I am creating a screen, adding a couple of LabelFields and no scrollbar, no scrolling at all. I am testing on 8900, OS 5.0.

Here is the code I use:

public class ExampleScreen extends MainScreen {

    public ExampleScreen() {
        super(Mai开发者_StackOverflow社区nScreen.VERTICAL_SCROLL | MainScreen.VERTICAL_SCROLLBAR);
        create();
    }

    private void add(String text) {
        add(new LabelField(text));
    }

    private void create() {
        add("line 0");
        add("line 1");
        ...
        etc
        ...
    }
}

The question is am I doing something wrong? Is there a way to enable vertical scrolling with MainScreen or do I need to create a VerticalManager myself?

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The LabelField(s) added to the screen should either be FOCUSABLE themselves, or you can add the following BETWEEN each of the label fields: add(new NullField(NullField.FOCUSABLE));