Bone jitters in reference layer

[Jkoseattle]

I have created a SMD for Head Up and Down. Works good. When I go into another project which references that character, this one SMD causes the character to jump all over the screen when this new bone is manipulated (both design and run time). No other bones in the rig have ever done this, just this one. Not only does the character jump around, the bone itself also jumps around, so I might move it up a little, and it jumps with the character, and also is suddenly pointing down. I've looked and looked at the source and everything works fine. Ideas?