Cisco WAN :: C887 15.1(3)T IPV6 CP Failure In PPPoA

My ISP is *starting* to roll out native-v6, quiet-like, and I'm trying to get it running in the ADSL-connected home-lab. However, for some reason, PPP link setup fails for v6; v4 is fine, as always. The argument which seems to be sent from IPV6CP as the link-ID seems like it might be overlong from some examples I've seen elsewhere.  I have seen 48-bit-ish examples, and this one is clearly longer.  I've not seen any config extracts that suggest I may have control over this, though.  At least not directly.I'd love to know where to look further, or if this is a known bug, but GOOG searches aren't giving me anything seeming relevant.  It's *possible* that the ISP needs to tweak something on the LNS side, but says he has another customer with a working setup (not necessarily on the c8xx ISR series hardware, though).  I had the same problems on c880data-universalk9-mz.124-22.YB8.bin image as well, and moved to the 15.1(3)T in hopes of better functionality.

Relevant config extracts:

boot system flash c880data-universalk9-mz.151-3.T.bin
! ...
ipv6 unicast-routing ipv6 cef
!...
! interface ATM0 no ip address no atm ilmi-keepalive pvc 0/32    encapsulation aal5mux ppp dialer   dialer pool-member 1 ! ! ...
! interface Dialer1 description PPPoA Dialer to ipHouse ip address negotiated ip mtu 1492 ip flow ingress encapsulation ppp dialer pool 1 dialer-group 1 ipv6 address 2001:4980:1000:1E00::2/64 ipv6 address autoconfig ipv6 enable ppp authentication chap pap callin ppp pap sent-username user@isp [snip]! ip forward-protocol nd

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