dhcp relay from a routing-instance

I have 2x srx5400 in active-passive cluster and the following topology

DHCPClients ----(172.23.58.0/24) reth1.58 SRX reth1.590 (172.23.59.0/25)----(172.23.59.15) DHCPserver

reth1.590 is in the master/default routing instance, reth1.58 is in a custom-VR routing instance.

Basically with the configuration from KB28642 i cannot get dhcp relay to work.

# run show dhcp relay statistics
Packets dropped:
    Total                      760
    No binding found           760

# run show dhcp relay statistics routing-instance custom-vr
Packets dropped:
    Total                      0

Messages received:
    BOOTREQUEST                764
    DHCPDECLINE                0
    DHCPDISCOVER               764

I've additionally enabled dhcp/bootp host-inbound-traffic on both client ingress and server ingress interfaces.

Setup should be almost identical to KB28642 except i'm using next-table stanza for routes from master->custom-vr. Other direction, custom-vr->master is covered with instance-import and policy-options.

I.e. routing between VRs works, hosts at 172.23.58.0/24 can access dhcp server at 172.23.59.15.

Actual config:

# show policy-options
prefix-list routes-from-master {
    172.23.59.0/25;
}
policy-statement accept-from-master {
    term ok {
        from {
            instance master;
            prefix-list routes-from-master;
        }
        then accept;
    }
    term reject-rest {
        then reject;
    }
}

# show routing-options
static {
 route 172.23.58.0/24 next-table custom-vr.inet.0;
}

# show routing-instances custom-vr routing-options instance-import
instance-import accept-from-master;

# show forwarding-options dhcp-relay
server-group {
    dummy-config;
}

# show routing-instances custom-vr forwarding-options
dhcp-relay {
    server-group {
        dhcp-srv {
            172.23.59.15;
        }
    }
    active-server-group dhcp-srv;
    group relay-in-vr {
        interface reth1.58;
    }
}

Any hints appreciated!