This thread is the source of the fix: http://comments.gmane.org/gmane.comp.kde.devel.bugs/1577991 The thrust of the discussion seems to be that it's better to disable libinput support altogether for now, so adjusting kwin's dependencies might be the safer bet. Reproducible: Always
Created attachment 395564 [details, diff] ebuild patch
Created attachment 395566 [details, diff] source patch
Created attachment 395578 [details, diff] fixes problem with new ABI of libinput I've solved it in a bit different way, did not pay attention to source of the event (wheel or fingers). Patch attached.
Created attachment 395594 [details, diff] fixes problem with new ABI of libinput Previous patch has typo.
https://github.com/gentoo/kde/commit/bc466b561f0df7598bbd28f20a9ee030fbcfe301