CentOS - Apr 2018 - touchpad stopped working in KDE only

I just installed CentOS 7 on a ThinkPad T420s.  All went well.  Touchpad
worked fine at login screen, in Gnome, and in KDE.  KDE is my preferred
environment, so I began customizing - including configuring the touchpad to
accept "Tapping" gestures via System Settings, Input Devices,
Touchpad.  As
soon as I hit "apply", the touchpad stopped responding to cursor
movements.  The touchpad buttons continue to work, just no cursor movements
with touches.  Touch pad is still fully functional at login prompt and in
Gnome.  However, cursor movements stop as soon as KDE desktop (KDE Plasma)
starts.

Any help would be greatly appreciated.  I'm almost ready to just re-install
CentOS 7 again and not mess with the touchpad settings ever again, but I
figure this must be something simple.  Other online solutions have not
worked, which is why I'm asking here.

Thanks,
TW