In Bryce, if you try to change any of the size axes of an object to a negative number, you are actually changing all size axes of that object to a negative number. If you'll check the Objects/Attributes for the last frame of your animation, I think you'll find that the size is -40,-40,-40, not -40,40,40. So naturally if you go from 40,40,40 to

-40,-40,-40 the center of the animation is 0,0,0. The way the geometry of the sphere is set up in Bryce, you can not mix negative sizes with positive sizes at the same time, because the sphere can not be a negative size and a positive size at the same time (think about it). I think the basic thing that's happening here is that you're turning the sphere into its own mirror image over time and also spinning it -180 degrees on the x rotation axis, but it would just shrink to nothing and re-expand to the original size...maybe if you had a texture that was oriented to the object (not the world) it would be mirror reversed in the last frame, I don't really know. I'm curious about what you want the animation to look like. Maybe you can do it through some other method than resizing the sphere. Hope this helps. :^)

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