Using an *external* DHCPv6 server for prefix-delegation in conjunction with PPPoE

[Frank Bulk]

I'm trying to get our lab bench Cisco 7206VXR (running 12.2(33)SRE2) to
cooperate with me in regards to using an external DHCPv6 server (ISC v4.2)
to delegate IPv6 prefixes to CPE.

Here's the relevant config snippets from the 7206VXR:

interface Loopback0
 ip address 192.168.99.1 255.255.255.0
 ipv6 address 2607:FE28:40FF::1/64
 ipv6 enable
!

interface Virtual-Template1
 mtu 1492
 ip unnumbered Loopback0
 peer default ip address pool pool-lns
 peer default ipv6 pool ipv6pool-lns
 ipv6 address autoconfig
 ipv6 enable
 ipv6 nd other-config-flag
 no ipv6 nd ra suppress
 ipv6 dhcp relay destination 2607:FE28:0:1000::7
 ppp authentication pap
!
ip local pool pool-lns 192.168.99.100 192.168.99.150
!
ipv6 local pool ipv6pool-lns 2607:FE28:4000::/56 64

Our DHCP server is reporting the following:
	Jan 10 17:17:13 node7 dhcpd: Relay-forward message from
2607:fe28:11:1000::1013 port 547, link address ::, peer address
fe80::9c0:e2eb:83e7:8467
	Jan 10 17:17:13 node7 dhcpd: [L2 Relay] No link address in relay
packet assuming L2 relay and using receiving interface
	Jan 10 17:17:13 node7 dhcpd: Unable to pick client prefix: no IPv6
pools on this shared network
	Jan 10 17:17:13 node7 dhcpd: Sending Relay-reply to
2607:fe28:11:1000::1013 port 547

So the CPE is making a DHCPv6-PD request, but apparently the DHCPv6 request
is getting forwarded without a link address.  I would have presumed the link
address would be from the 2607:FE28:4000::/56 address space.  I've use both
a D-Link DIR-615 and Cisco 871W as CPE, but not getting any success.

Any ideas?  Is anyone else doing this?!?

Frank