It could be a grouping error of some sort. It can also be a jp issue, but my first guess is it has something to do with the grouping. It can be fixed by regrouping that part of the dress. (if it IS a grouping problem)

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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.