a couple of days ago I had a system update the included plasma 5.5.5 and also Chromium to 49.0
I’ve noticed that since then Chromium now has smooth scroll enabled. I can’t find any setting to turn it off in Chromium or indeed if smooth scroll is specified by Chromium or an update in Plasma.
Anybody have any ideas on this?
Based on a quick Google search “chromium smooth scroll” it’s probably implemented as an Extension, so it’s logical you should be able to go to your list of installed extensions in your browser and either disable or uninstall.
TSU
nope - no smoothscroll extension installed (only extns installed are; Hangouts, google translate, ublock origin, ymp one click installer)
it has only been evident since the upgrade to plasma 5.5.5 and chromium 49.0.2623.75, so one of those is surely the culprit.
ok . . . so I just rolled back to Chromium 48.xx from the oss repo and smoothscroll has gone . . . .
so it seems smoothscroll has definitely now been hardcoded into Chromium as of version 49.xx.
Now I just need to learn how to shut it off.
just do chrome://flags in the address bar of chrome/chromium, and you will see a list of thing you can disable, one of which being smooth-scrolling 
that did it - thanks