A recent change to make routing more tightly timed with the PPP link on our broadband lines means any customers that are not negotiating IPV6CP are not getting IPv6 routing at all.
Previously we were being technically incorrect routing traffic without IPV6CP negotiation completing.
Examples are customers using pppd on linux based equipment.
The solution is to add +ipv6 to the config for the peer.
Please ask for more advice on irc if you have any issues.