Configuration problem with IPv6 router ("cannot forward src")

[Bruce Cran]

I'm trying to set up a IPv6 router (running -current) on my home 
network. My ISP gives me a /128 via PPP and I have a /48 allocation, 
which I use to give em0 and tun0 public addresses in different subnets 
(tun0 is assigned the address via ppp.linkup).
I've added all the IPv6 settings to rc.conf (ipv6_gateway_enable, 
ipv6_network_interfaces, rtadvd_enable etc.) and I can ping IPv6 sites 
from the router.

The problem is that rtadvd continues advertising the default gateway as 
tun0's link-local address - and pinging from a machine on the network 
results in "cannot forward src" messages on the router (strangely, 
despite hisaddr being fe80::205:... in ppp.log, the kernel logs the 
address as fe80:f::205:...).

Is there some extra configuration I've likely missed that's needed when 
using IPv6 via PPP?

-- 
Bruce Cran