I'm a little baffled by this report, but I don't at all suspect it's inaccurate. I'm on the same version of Chrome on OSX on a macbook air (where I developed the custom scrollbar). Programmatically, I'm using the "scroll wheel"'s delta increment to determine the distance to scroll--the same amount in both directions. If anyone with relevant experience developing JS interaction with the scroll wheel has any hints or related knowledge, I'd love to hear it.

Thanks for the thorough feedback and videos. Looking forward to making the scroll bar perfect!