Initial jump in the opposite direction when scrolling

[hife]

System: Ubuntu 16.04, Unity environment
Hardware: Touchpad with two-finger scrolling enabled
Program version: qpdfview 0.4.15

Steps to reproduce:

1. Open a multi-page pdf document in qpfview.

2. Scroll to a position in the middle of the document (so there is room above and below the visible part).

3. Go to another program window and do some typing (or maybe just wait for a while).

4. Move the mouse over the qpdfview window and move up or down with two fingers.

Expected behaviour: The document view scrolls in the direction you move your fingers in.

Actual behaviour: The document view jumps a varying length in the opposite direction of your movement before scrolling in the intended direction.

The jumps vary between a few lines and close to a full page. Either way, it is extremely disorienting.

This does not happen in Evince or any other program.

I have not been able to pinpoint the exact conditions under which the problem occurs, I am usually typing notes in LyX while having both the qpdfview and LyX windows on screen next to each other, and when trying to scroll the document (without giving focus to the window), the jump happens.

[Mans Rullgard (mansr)]

I'm seeing this using a regular mouse with scroll wheel as well. The first click of the wheel after focusing qpdfview often scrolls in the wrong direction.

[Louis-Philippe Véronneau (pollo-debian)]

It seems the same bug happens in Debian:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=807115