... On the other hand, it's possible to see the same thing happen when moving the pointer between the discussion index slide-in panel and a discussion. It's possible to get the discussion scrolling up and down while the pointer is over the slide-in panel.
This may have more to do with how the browser handles focus than anything. I'm using Safari 9.1.1 on Yosemite. Which browser are you using Bek ?
@Toby What do you think? Is this within tolerances? Or does it merit a look?