When the DHD detects that the "page" is long, when you do an initial scroll (say a flick with your finger), the "scroll" on the side suddenly "enlarges". While this is there (a delay of about 2 seconds I'd say), tap and hold the "enlarged" button, and this will make a "fast scroll".

Hope that helps ^^

 

If you mean the page suddenly flicks down when you are scrolling. Mine does that, it's very annoying, I think it's a glitch or something.