I think I've found the problem.  Ever wonder what that "flipped" line in the joint listings does?  Well, one thing it does is cause this problem, if it's there when it shouldn't be.

As far as I can tell, "flipped" should be present in the otherActor affector listings for a joint (such as shoulder twist in collar), but never, ever present in the joints for the actor itself.  I had exnded up with them incorrectly in place when I recreated my joint listings for some actors by pasting those otherActor affectors back in as main joint/twist listings in the actor.  I didn't remove flipped.  So Poser was confused, and part of the time it was apparently trying to reverse the effect of the joint or something.  Whatever flipped does.  :unsure:

===========================sigline======================================================

Cage can be an opinionated jerk who posts without thinking.  He apologizes for this.  He's honestly not trying to be a turkeyhead.

Cage had some freebies, compatible with Poser 11 and below.  His Python scripts were saved at archive.org, along with the rest of the Morphography site, where they were hosted.