rtadvd: no temporary address on interface

Hello,

background: running a small router/firewall appliance based upon FBSD 14-STABLE/IPFW.

My ISP provides ::/56 prefixes. Setting up tun0 via mpd5 with KAME dhcp6c (net/dhcp6) and a
textbook standard setup for prefix delegation seems to work. The router's ISP facing interface
is desinated tun0, several (vlan) NICs are facing towards our inner network, each NIC serving
a different network and getting its dedicated prefix.
On the router's system, the following MIBs are set:
net.inet6.ip6.use_tempaddr: 1
net.inet6.ip6.prefer_tempaddr: 1

Although setting such MIBs on any FreeBSD machine we maintain results in setting IPv6 not
using the encoded MAC address within the lower 64 bit of the NIC's IPv6 address, I didn't
manage to force rtadvd(8) to provide a "temporary" IPv6 address.

The NICs obtain delegated prefixes and addresses obviously via SLAAC/EUI64.

Is this behaviour a bug? Or do I misunderstand some concepts of FreeBSD and IPv6? Or is it
simply a misconfiguration?

Thanks in advance,

Oliver

-- 

A FreeBSD user