Re: Single-session dual-stack subscribers - how it works?

And finally working config is 

dhcpv6 {
    overrides {
        delete-binding-on-renegotiation;
        dual-stack DS;
    }
    group ipv6-stacked-subscribers {
        interface demux0.0;
    }
}
pool-match-order {
    ip-address-first;
}
duplicate-clients-in-subnet incoming-interface;
overrides {
    client-discover-match incoming-interface;
    dual-stack DS;
}
group ipv6-stacked-subscribers {
    interface demux0.0;
}
dual-stack-group DS {
    authentication {
        username-include {
            user-prefix DUAL-STACK;
            interface-name;
        }
    }
    dynamic-profile IP-DHCPv4-DHCPv6;
    classification-key {
        mac-address;
    }
    protocol-master inet;
}

Problem was with overrides settings, which not inherits settings from overrides statement up one level.