Touchpad two-finger scrolling glitches in Discover

Plasma-discover seems unable to interpret _upwards_ scrolling with a touchpad that has two-finger scrolling enabled. Scrolling works _downwards_, but when I reach the end of an app list it refuses to scroll up.

Steps to reproduce:
1) Obtain a laptop with a touchpad that support two-finger scrolling.
2) In systemsettings -> Input devices -> Touchpad -> Scrolling enable Two-Finger Scrolling.
3) Open Discover and go to any category. Attempt to use two-finger scrolling to scroll down. Then try to scroll up. Scroll to the bottom and attempt to scroll up again.

Only happens with two-finger scrolling; edge scrolling works fine. Same glitch appears whether Inverted Scrolling is enabled or disabled.

a) Kubuntu 17.10 Daily, updated as of 09102017, installed to harddrive.
b) Plasma-discover version 5.10.5-0ubuntu1

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: plasma-discover 5.10.5-0ubuntu1
ProcVersionSignature: Ubuntu 4.13.0-12.13-generic 4.13.3
Uname: Linux 4.13.0-12-generic x86_64
ApportVersion: 2.20.7-0ubuntu2
Architecture: amd64
CurrentDesktop: KDE
Date: Mon Oct 9 12:17:59 2017
EcryptfsInUse: Yes
ExecutablePath: /usr/bin/plasma-discover
InstallationDate: Installed on 2017-09-22 (16 days ago)
InstallationMedia: Kubuntu 17.10 "Artful Aardvark" - Alpha amd64 (20170922)
ProcEnviron:
 LANGUAGE=nn:nb:en_GB:en_US
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=nn_NO.UTF-8
 SHELL=/bin/bash
SourcePackage: plasma-discover
UpgradeStatus: No upgrade log present (probably fresh install)