Attached Link: http://yarchive.net/space/spacecraft/gimbal_lock.html

My guess is that it has to do with the way/order that the joint rotations are applied. I've seen this before in 3D Studio MAX. (The phenomena is similar to a "gimble lock" that mechanisms such as gyroscopes can experience.) It might be possible to fix it if the base orientations of the joints can be changed. I just don't have the time or energy to dig into it right now. Looks as if I'm going to have to scrap Poser for this project and dust off my trusty old copy of Humanoid. Cal