all 'moves' are rotation. The only bone to get a translational move is the root bone. The effect I found was caused by rotation.

I can't pin down a specific cause.....but certain bones rotated a certain way seem to cause an issue with mounts...namely the ride switching rapidly from facing front to facing backwards.

Odd fact number 2 was that it didn't affect all animations for a given skeleton...

Odd fact number 3 was that certain bones seem to have issues when you come to edit them, which is why I now build from scratch, rather than trying to edit an existing one...

Odd fact number 4... the horse anims are SCREWED... I thought I had messed something up in my anim pack, so I re-installed and re-did it...but no...it's the originals. Some of the animations when imported do stupid things. I have avoided doing any edits on those...since I doubt very much that I will get good results editing something that clearly has issues

Anyway....I don't know if this a side effect of the differences between the method CA used as opposed to XIDX or what..... but I managed to work around the problem for now.