The displacement side-effect mentioned above is not a bug in the yCenter channels. The same occurs, when you modify the ordinary Poser Origin. Suppose you have carefully arranged your arrow prop in the scene. Then you want to modify the origin a little bit. So you change the origin data just a little bit, but the stupid prop drifts from its position, and you can start all over again. This annoying "phantom motion" is not a Poser bug, it's the effect of re-evaluated rotations (or scales). The phantom motion occurs, whenever a rotation (or scale) channel is set, and then a new origin is defined. The preexisting rotations (and scales) are differently evaluated, to reflect the new center of rotation. Because of this, the prop is displaced and re-positioned, which looks like a spooky translation. The example arrow shown has a preexisting rotation, that is, zRotate is 45. The origin is at the upper end of the arrow (y=1). When you move the origin to y=0.5, the center of rotation moves towards the ground. Since the new center of rotation (y=0.5) lies in the center of the arrow body, the arrow moves, to bring its center to the position of the new origin. In this case, the phantom motion looks like a translation along the y and x axes.