Bug (probably): Mixing IPv6 PD on PPPoE and RA (ULA) config on Ethernet

I've been trying to configure IPv6 ULA addressing on my network alongside the IPv6 delegated prefix from my ISP. As I understand the RFCs, there's nothing stopping a host or a router having multiple addresses from different ranges.

Initially I had this config on my PPPoE interface:

ethernet eth0 {
     address 10.255.255.1/31
     duplex auto
     mtu 1508
     pppoe 0 {
         default-route auto
         dhcpv6-pd {
             pd 0 {
                 interface eth2 {
                     host-address ::1
                     no-dns
                     prefix-id :0
                     service slaac
                 }
                 prefix-length /56
             }
             prefix-only
             rapid-commit enable
         }
         firewall {
             in {
                 ipv6-name Internet-Inbound6
             }
             local {
                 ipv6-name DirectToRouter6
                 name DirectToRouter
             }
         }
         ipv6 {
             address {
                 autoconf
             }
             dup-addr-detect-transmits 1
             enable {
             }
         }
         mtu 1500
         name-server auto
         password spoons
         user-id edgerouter@btbroadband.com
     }
     speed auto
 }

This works fine, and I have public GUA addressing on my internal devices, all good so far.

Then I add a ULA address on my internal interface with RA:

ethernet eth2 {
     address 172.16.0.254/24
     address fdee:eeee:eeee:0::1/64
     duplex auto
     ipv6 {
         router-advert {
             cur-hop-limit 64
             managed-flag false
             other-config-flag false
             prefix fdee:eeee:eeee:0::/64 {
                 autonomous-flag true
                 on-link-flag true
                 valid-lifetime 2592000
             }
             reachable-time 0
             retrans-timer 0
             send-advert true
         }
     }
     speed auto
 }

At this point I lose my GUA addresses. I've checked the radvd.conf file and it looks like it is overwriting the PD config with the ULA config. It has also been shown that if I delete the ULA config from Eth2 it doesn't reinstate the PD config from the PPPoE interface, so at that point the CLI doesn't match the underlying radvd configuration.

The problem I'm actually trying to solve is having fixed ways to reference internal hosts when I have a dynamic IPv6 prefix, I thought ULA might be a good way...

Matt