scrolling without last line

hello

I can't manage scrolling

this is quite weird. I have a button with this action:

controller.verticalScrollPosition+=controller.getScrollDelta(1);

it works fine until the last line of text (which is always invisible). Then it stops and cannot event move back by:

controller.verticalScrollPosition-=controller.getScrollDelta(1);

just won't work. textFlow is as simple as possible

textFlow = TextFilter.importToFlow(markup, TextFilter.TEXT_LAYOUT_FORMAT);

but if I import a plain text

textFlow = TextFilter.importToFlow(markup2, TextFilter.PLAIN_TEXT_FORMAT);

scrolling doesn't work at all.