Down arrow scrolling on safari 'sticking'?

I'm not sure how to describe this - sometimes (not predictably but frequently) when I'm scrolling down a webpage using the down arrow, I'm tapping the arrow and it's going down just a bit (absolutely fine), but then it suddenly just goes for it and I can't stop its momentum by tapping up or clicking. It stops where it wants to stop.

So if I press up or down, 90% of the time it moves the page maybe an inch; but then next time it might scroll me all the way to the bottom of the screen. It's only a small thing, but it's really irritating when I'm trying to read or skim a list.

I've only noticed it maybe the last 6-8 months (not linked to an update as far as I can recall). I've checked there's nothing making the key stick, and I can't find any 'sticky key' equivalent options in the menu. And it doesn't seem to be a 'long press' issue... any suggestions?