I've always assumed it was a sort of Error - like "out of bounds" thing. As far as I can tell it doesn't REALLY matter. At least i've had it quite a few, otherwise working, rigs :)

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.