Wow, yeah just tested that and it's really bad. I guess it's a strange thing to do, but a good way to test how the cursor hijacking code gets stalled when scroll is active, and I'm guessing they're doing UI updates on scroll so the thread is getting thrashed there.

Even just making a circle motion with a mouse produces a lot of stuttering. I just did the same action on HN and it's as smooth as you'd expect on a CPU from 1995 and beyond.