spline controller system + rotation

hi, im using the spline controller system ( http://goo.gl/rnD28O ). then rotation script ( http://goo.gl/JnDpEV ) assigned to gameobject as child of "spline system follower".

when its global direction is constant, rotation works fine. but when direction of follower changes(cuz of waypoint nodes' placements) rotation goes crazy and loses the rotation script control.

i was using parent-child system to set the pivot point of rotation (using localRotation in script). you guys have any idea why it happens? is there a proper way to use rotation on a waypoint following object?