You can reproduce it by trying to use the scroll wheel to scroll down halfway and then back up. Despite the mouse wheel (or the touchpad as well) scrolling up, the contents still scrolls all the way to the bottom.
I can confirm that new systemsettings has messed up scrolling. Mouse: slow as hell but otherwise ok (I've heard that there is a Qt bug for that). Touchpad: speed is ok, but it is going in random direction. Trackpoint: same as with touchpad. Every other application is fine, for example: dolphin, firefox.
Seems reminiscent of https://bugs.kde.org/show_bug.cgi?id=380511
*** This bug has been marked as a duplicate of bug 384508 ***