Wow. Could be several things I suppose. Don't know how good a typist you are, but if I try to type real fast I make mistakes and hit the backspace fairly often. If you were typing and brushed the track pad and focus got taken out of the text box, backspace would take you back a page. I've had the problem of typing in a box and when I brush the pad, focus gets taken elsewhere on the page. Just one guess... I guess.
If this is the problem, maybe there is a way to adjust the sensitivity of the pad.