IPv6 SLAAC Global Address Assignment over PPP using SRX300

Hi all, 

I'm currently attempting to configure an SRX300 as dual stack, using an FTTP connection. The IPv4 works fine, PPP authenticates and the LNS (Cisco ASR) assigns the addressing correctly.

The issue I'm having is with IPv6 and the set up for using SLAAC to have a gateway assigned to the pp0.0 interface to route between the ASR and the SRX. The ASR has a /48 subnet for assigning /64s as auto config gateways and this works absolutely fine on Cisco devices. I've yet to get it working with an SRX. I've been unable to determine if there are any know issues with SLAAC on an SRX using a pp0 interface, so I'm assuming it does but let me know if otherwise.

2a00:f18:19:9::/64 is the subnet I'm statically configuring on the LAN and there is a static route on the ASR installed when the PPP session comes up. Here's the configuration from my SRX, with unrelated config removed:

version 15.1X49-D45;
security {
    forwarding-options {
        family {
            inet6 {
                mode flow-based;
            }
            mpls {
                mode packet-based;
            }
        }
    }
}
interfaces {
    ge-0/0/0 {
        description LAN;
        mtu 9192;
        unit 0 {
            family inet {
                mtu 1500;
                address 192.168.0.1/24;
            }
            family inet6 {
                address 2a00:f18:19:9::1/64;
            }
        }
    }
    ge-0/0/5 {
        description SUPPLIER;
        unit 0 {
            encapsulation ppp-over-ether;
        }
    }
    lo0 {
        unit 0 {
            family inet {
                filter {
                    input management;
                }
            }
            family inet6 {
                address 2a00:f18:19:9::fffe/128;
            }
        }
    }
    pp0 {
        unit 0 {
            ppp-options {
                chap {
                    default-chap-secret "[PPP-PASSWORD-OMITTED]"; ## SECRET-DATA
                    local-name "[PPP-USERNAME-OMITTED]";
                    passive;
                }
            }
            pppoe-options {
                underlying-interface ge-0/0/5.0;
                idle-timeout 0;
                auto-reconnect 3;
                client;
            }
            family inet {
                mtu 1492;
                negotiate-address;
            }
            family inet6 {
                mtu 1492;
            }
        }
    }
}
routing-options {
    rib inet6.0 {
        static {
            route 0::0/0 next-hop pp0.0;
        }
    }
    static {
        route 0.0.0.0/0 next-hop pp0.0;
    }
}
protocols {
    router-advertisement {
        interface pp0.0 {
            managed-configuration;
            prefix 2a00:f18:19:9::/64 {
                no-autonomous;
            }
        }
    }
    neighbor-discovery;
}

Here's an output of the RA I'm getting from the ASR, which has selected 2a00:f18:4:18::/64 from its /48 pool:

show ipv6 router-advertisement
Interface: pp0.0
  Advertisements sent: 19, last sent 00:00:31 ago
  Solicits received: 0
  Advertisements received: 11
  Solicited router advertisement unicast: Disable
  Advertisement from fe80::72ca:9bff:fe74:e700, heard 01:34:55 ago
    Managed: 0 [1]
    Other configuration: 0
    Link MTU: 1492 bytes
    Reachable time: 0 ms
    Default lifetime: 1800 sec
    Retransmit timer: 0 ms
    Current hop limit: 64
    Prefix: 2a00:f18:4:18::/64
      Valid lifetime: 2592000 sec
      Preferred lifetime: 604800 sec
      On link: 1
      Autonomous: 1

Thanks for looking, appreciate any pointers anyone is able to give. If any further information is required, please ask.