[Dell XPS 13] Trackpad two-finger scroll makes cursor move when scrolling up

Steps to reproduce on Dell XPS 13 L322X:

1) Turn on two-finger scrolling
3) Open a long web page or document
3) Scroll down (drag two fingers down the pad)
    The page scrolls easily and the cursor doesn't move (desired behaviour)
4) Scroll up (drag two fingers up the pad)
     The page does scroll, but the cursor continually jumps upward in steps during the scroll and more swipes are required to scroll up than down.

Effect: An up scroll more difficult to accomplish than a down scroll.

Probable cause: Up scroll gesture is misinterpreted as a cursor movement?

Expected behaviour:

When scrolling up the cursor should not move and it should be as easy to scroll up as it is to scroll down. In other words, the cursor should behave in the same way when scrolling down as when scrolling up.

Affects:

12.04.3, 13.04, 13.10

As a side note, on 13.10 if 'Natural scrolling' is turned on to flip the gesture direction, this problem occurs the other way around demonstrating that this is a software issue. That is, the cursor jumps when scrolling down, but does not jump when scrolling up.