Actually otherwise.  The sig would be invalidated, which I think is wrong.
The right thing for your case would be to let it be as it is.

If a port range has been specified, the right behaviour would be -
1. If sig port range UNION PP port range = PP port range, reduce sig port range to PP port range.
2. If sig port range UNION PP port range = sig port range, don't touch it.
3. If the sig port range UNION PP port range != both sig port range or PP port range, invalidate the signature.

Sounds right?