Calculated property gives error but works...

Hi,

To count gamepieces in a deck I use a dummy piece with a textlabel $_numPieces$ but this counts also the dummy piece.
So I add a calculated property in the dummy piece with name ‘HowManyCards’ and expression $_numPieces$-1 and put $HowManyCards$ in the textlabel. The count works and is correct but I get

Bad Data in Module: Expression evaluation error chit-woodback-Calculated Property[HowManyCards]={$Wood_numPieces$-1}, Error= inline evaluation of: ``_xyzzy=_plugh();’’ internal Error: Unimplemented binary String operator

in the log window. Can I just ignore this because it works or will I end up with even more problems? Is there another way to count the pieces in my deck (without an at-start-stack underneath)?

tia

Dont put your dummy piece in the deck. Keep it on the same map though off to side somewhere