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.
I've now got ipv6 glue in the roots for pointless.net, and changed to secondary nameservers that are on ipv6, and also do dnssec.
The only thing thats missing is that the blockhosts script (and anti ssh scanner script) dosn't seem to do ipv6 properly, I'll fix it when i get a chance.
I can really recommend the Hurricane Electric tunnel service, it's really straight forward to get running and the certification is a great learning aid.