Recently my mid 2012 Retina Macbook Pro's trackpad has started exhibiting some strange behavior. Attempting to scroll up or down using the two finger gesture randomly seems to trigger the page back/page forward gesture.
I've tried rotating my macbook slightly to correct for any slight variation in my finger positioning, however that doesn't seem to help.
I don't know the exact point where this began happening, but I'm sure it wasn't like this a year ago. I'm currently running Yosemite, after upgrading from a clean install of Mavericks.
Edit: This is primarily happening in Google Chrome. I will try other browsers but I suspect this is irrelevant.
Best Answer
If this is happening in Preview: when your pointer is on the titlebar/toolbar, using the 2-finger scroll will trigger the page up page down gesture. Make sure your pointer is on the document itself and not the titlebar.