Here, have some system output, slightly sanitized.
7.10 VE that works:
relevant ifconfig output:
venet0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
inet addr:127.0.0.1 P-t-P:127.0.0.1 Bcast:0.0.0.0 Mask:255.255.255.255
inet6 addr: ::1/128 Scope:Host
inet6 addr: 2001:470:x:x::x/0 Scope:Global
relevant /etc/network/interfaces settings:
iface venet0 inet6 static
address ::1
netmask 128
up ifconfig venet0 add 2001:470:x:x::x
ipv6 routing information:
::/0 :: U 256 0 0 venet0
::1/128 :: U 0 6 1 lo
::1/128 :: U 0 0 1 lo
2001:470:x:x::x/128 :: U 0 372 1 lo
ff00::/8 :: U 256 0 0 venet0
----------
9.04 VE not working:
relevant ifconfig output:
venet0 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00
inet addr:127.0.0.1 P-t-P:127.0.0.1 Bcast:0.0.0.0 Mask:255.255.255.255
inet6 addr: ::1/128 Scope:Host
inet6 addr: 2001:470:x:x::x/128 Scope:Global
relevant /etc/network/interfaces settings:
iface venet0 inet6 static
address ::1
netmask 128
up ifconfig venet0 add 2001:470:x:x::x
IPv6 routing information:
::/0 :: !n -1 144448555 lo
::1/128 :: Un 0 1 4 lo
::1/128 :: Un 0 1 0 lo
2001:470:x:x::x/128 :: Un 0 1 3 lo
ff00::/8 :: U 256 0 0 venet0
::/0 :: !n -1 144448555 lo
----------
Obviously the default route statements on the 9.04 system stink. This is where I'm stuck.