Ah, yes, I see that the Body xTran, yTran, zTran suddenly change when I move to the problematic frame. I don't know how, because I always put the actor into the space by translating and rotating the hip; maybe I used the "Body" coordinates by accident once. Thank you, I am happy to have been guided to this clue. Now I just need to back out what all the coordinate systems are in Poser. I wish there was a way to display all the coordinate systems for visualization.