Jerky NSScrollView scrolls to a specific angle on Yosemite (when using layers)

I have an NSScrollview with a large canvas that can be scrolled and scaled, etc. When I scroll diagonally at an angle of about 20 degrees from vertical, it really jerks (using the track pad). This dash even continues as the rest animation scrolls.

All other scrolling corners have a buttery smoothness, which makes me think it has something to do with a vertical scrolling preference (axis predominant scrolling is disabled).

The effect seems to only happen when I use layers with layer support.

Does anyone know what's going on here?

thank

Craig