Scrolling issue (zooms w/ one finger)

[totalkaose]

I've recently started having this problem; when I quickly scroll across a page/photos it will zoom in. It also seems to dart through the page, like shoot down to the bottom if I click on something. Its been doing it a bit since I can remember (got a referbished phone a few months ago) and now its so much worse.
I'm wondering if its the sensor in the phone or something else. I could use some help, or advice. Thanks!