Ipv6 on separate interface not working until router is ping'ed?!?

[dopey]

This is weird.  I have centurylink fiber using 6rd for ipv6.

I have a second LAN interface (OPT1) that i enable ipv6 on (track interface, with it's own prefix ID unique from LAN)

Whenever the router reboots, machines on the second interface get allocated IPv6 addresses fine (i'm not using dhcpv6) but I can't connect to any ipv6 addresses.
tracepath6 basically stops at LOCALHOST (no reply from antying past my host) which seems to imply RA isn't working right.

If I ping the router's OPT1 IPv6 address, everything magically starts to work.

I have a firewall rule to allow OPT1 net addresses ipv6 traffic already.

Any ideas why pinging the router from the host magically allows things to start working?

[dopey]

Hurm. definitely related to RA.

ip -6 neigh (from a linux system) doesn't show any routers prior to pinging the router ip.

after pinging the interface's ipv6 address on the router everything works and ip -6 neigh shows the router as reachable