Drawn circle offset from points

In event 2 when measuring the "middle" particle track (second from the left in the cartoon), the drawn curve is usually the right curvature, but always offset about 20 pixels perpendicular from the actual trace.

This does not appear on any mostly vertical or horizontal traces. It also shows up when marking similar points towards the middle of the image.

Another student observed it when doing a short measurement for the 4th track from the left in event 1.