How about inverse kinematics? I've seen strange things happen when inverse kinematics are turned on - legs going all wonky, arms flying off into space. With IK turned off the preview seems to behave better. And how does the RENDER work? Is it just a preview issue, or do the renders also get mixed up? If it's only preview, you might want to change the OpenGL settings. I use OpenGL hardware, seems most stable on my machine. Others use OpenGL software or Sree3D. Anyway, I wish you luck! This kind of thing is pretty tough to figure out.

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