Comment 0 for bug 1214385

/sbin/dhclient-script in precise's isc-dhcp-client 4.1.ESV-R4-0ubuntu5.8 contains the following snippet:

    BOUND6|RENEW6|REBIND6)
        if [ -z "${new_ip6_address}" ] || [ -z "${new_ip6_prefixlen}" ]; then
            exit_with_hooks 2
        fi

        # set leased IP
        ip -6 addr add ${new_ip6_address}/${new_ip6_prefixlen} \
            dev ${interface} scope global

This assumes that the result of the DHCPv6 transaction is an address with a prefix, which is the case for stateful DHCPv6. For stateless DHCPv6, however, we only get additional information that's not directly address-related. This is fixed in saucy and reads like this:

    BOUND6|RENEW6|REBIND6)
        if [ "${new_ip6_address}" ] && [ "${new_ip6_prefixlen}" ]; then
            # set leased IP
            ip -6 addr add ${new_ip6_address}/${new_ip6_prefixlen} \
                dev ${interface} scope global
        fi

It looks like the only change from the diff to the current saucy version we need for it to work correctly.