It wasn't actually the blockhosts script that was the problem, it was the tcpwrapper libwrap trying to convert text ipv6 addresses to ipv4 addresses, so I get a lot of these in the logs:
warning: /etc/hosts.allow, line 14: unable to convert [ipv6 address] to address
That's annoying but harmless.
What's more of the problem is that spamcop doesn't support ipv6 addresses in email headers, and since I have an ipv6 connection to my server when I'm at home and in the space I get most of my mail over ipv6.
So I can't report spam any more, not that it would of made much difference, but it was satisfying.