As Kuroyume mentioned, you can edit the PP2 file to decide
on which scale controls the others.  It's not hard at all; just
find the parent part, and change the lines as follows:

propagatingScale Scale
to
scale Scale

propagatingScaleX xScale
to
scaleX xScale

and similarly with the Y and Z.

You can also do this inside a PZ3 if you have, for instance,
a human figure parented to a chair, and you want to be 
able to rescale the chair without distorting the human.

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