This is well known ERC behavior.

There is a way to fix it (needs some work, however). What you have to do is create a second FBM dial on the body with a different internal name.
Example: the ShouldersThickness morph. You will have this code in your CR2:

actor rCollar:1
{
    channels
    {
        ...
        targetGeom PBMShouldersThickness
        {
             ...
            valueOpDeltaAdd
            Figure
            BODY
            PBMShouldersThickness
            deltaAddDelta 1.00000

Now add a second block of ERC slaving code

            valueOpDeltaAdd
            MyShirt                            //the name of your figure, NOT Figure, or Figure 1 
            BODY:1                          // include the number, unlike in the previous block
            PBMShouldersThicknessLocal      // the internal name of the extra FBM
            deltaAddDelta 1.0000

And in the BODY actor, create a second set of valueParms with the same names as the original FBMs, but with "local" appended to their internal name:

        valueParm PBMShouldersThicknessLocal
       {
            name ShouldersThickness
           ...
     
Lastly, hide the "original" FBMs in the BODY actor.

Should do the job.

Another option might be using linkParms statement in the Figure section. linkParms is an older way of slaving morphs to FBM dials, with much less control (you cannot change the valueOp type or the detalAddDelta value), but with the advantage that it never crosstalks - linkParms only work within the same figure.

     

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