I have the same problem and am completely clueless as to why it happens. However the work-around I'll be doing is to set a keyframe at 1 second and animate from there. That way I have a "real" reference to work from. And when things get really weird, I go to frame zero and get the misbehaving bone's info (xyz location and rotation) and then apply it manually to the bone in the frame that's giving me problems. In fact, for most models I've skinned, I made a map of the skeleton, by hand on paper, with all that info written in. It's a handy reference that has helped me in the past. Maybe one thing that's adding to this problem is the way that I make the left and right sides (for arms and legs) - I select the parent bone (hipLeft or shoulder left) and go to the edit menu and choose duplicate with symemtry(sp) and then change the name in the property panel -- changing left to right. On bones that have been created this way the check box for "mirrored" is checked. Maybe that's getting C confused? Haven't tried that out as I'm in the middle of creating a rig and figuring out the IK helper tool. HTH mike rhodes