Endesmanreported this bug
When changeparent is used in a pose other than base pose, there is a very weird offset for a fraction of second. The usage is to transition between a pose that was animated for a rigged model, vs an unrigged model, for the death of my mega-skeleton.
This issue might have something to do with the former step-keyframe issues, since the transition between one method of animation and the other (which occurs simultaneous to the changeparent) is also done via step keyframes.