The 'cpty' field is for internal memory management purposes only.
No client can know of its existence, let alone inspect or directly
change the value, so it should not be used to adjudicate control set
equality. This was useful during the refactoring work to introduce
the opm-parser support, but its utility has since ceased.
Okay'ed by: [at] atgeirr and [at] joakim-hove