The generating code does this:
https://github.com/BNFC/bnfc/blob/master/source/src/BNFC/Backend/C/CFtoCSkel.hs#L85

But, the calling code does this:
https://github.com/BNFC/bnfc/blob/master/source/src/BNFC/Backend/C/CFtoCSkel.hs#L245

These are not the same since the first uses islower on the tail. The result is an invalid skeleton.