I'm thinking that at some point, certain apps including Chrome added a built-in keystroke of "Ctrl-V" for something like "Vertical Scroll", but only recently. I can't find Ctrl-V in their menus. Ideally I would find that menu item and remap it to swizzlestick-V, but since it's not a menu item I can't find it or remap it.

I still only reproduce the problem on Chrome and Safari, I can't find other apps that do it yet. But I'll bet they exist.