Help with quagga BGP config for ipv6 route-server

[djw at bbn.com (David Waitzman)]

I am trying to set up BGP peering with a route-server, concurrently dual-stack.  BGP 4 over an IPv4 connection works fine.  A separate BGP 6 over IPv6 fails: with an "[Error] No common capability".  

I am using quagga 0.99.20 on ubuntu 10.04.03.   I don't know what the route-server is.
I have tried to tell both quagga to not be strict about capabilities or not negotiate them at all.

My quagga config includes:
router bgp XX
no bgp enforce-first-as
no bgp default ipv4-unicast             !! tried with and without this

bgp router-id XX
network XY/24 route-map SetAttr

neighbor XX4 remote-as XX
neighbor XX4 activate
neighbor XX4 next-hop-self
neighbor XX4 send-community

address-family ipv6
network XY6/48 route-map SetAttr
neighbor XX6 remote-as XX
neighbor XX6 activate
neighbor XX6 next-hop-self
neighbor XX6 send-community
neighbor XX6 soft-reconfiguration inbound

The code, I think, that's triggering the error is:
/* Check there is no common capability send Unsupported Capability
    error. */
 if (*capability && ! CHECK_FLAG (peer->flags, PEER_FLAG_OVERRIDE_CAPABILITY))
   {
     if (! peer->afc_nego[AFI_IP][SAFI_UNICAST] 
         && ! peer->afc_nego[AFI_IP][SAFI_MULTICAST]
         && ! peer->afc_nego[AFI_IP][SAFI_MPLS_VPN]
         && ! peer->afc_nego[AFI_IP6][SAFI_UNICAST]
         && ! peer->afc_nego[AFI_IP6][SAFI_MULTICAST])