Some (mainly older ones, afaict) touchpads have additional buttons to the
usual LMR set. These buttons are usually used for up/down and left/right
scrolling.
Something like this:
http://www.hardwarezone.com/img/data/articles/2002/591/touchpad_keyboard.jpg
If you own a laptop with such a touchpad, please contact me off-list, I'd
like to get some logs from you.
Cheers,
Peter