route advertisement question

Hello

I am hoping that someone can give me some perspective with a problem I was recently
troubleshooting.

I have a small network with several machines on the network. This network runs both IPv4 and IPv6,
however the router on the network is IPv4 only. Therefore IPv6 is used on the local network and
not routed off network. On one machine I am running OpenBSD 7.0 release and have rad(8) running
with the config below...

#cat /etc/rad.conf
default router no
interface re0 {
prefix 2001:db8::/64
}

For reference the interface config is this...

#cat /etc/hostname.re0
inet 192.168.1.5 0xffffff00
inet6 2001:db8::53 64

On another machine I am running OpenBSD 7.0 current with the interface config of...

#cat /etc/hostname.re0
inet autoconf
inet6 autoconf
up

On the 2nd machine the re0 interface never gets the autoconfigured 2001:db8::xxx address. I have
made sure that slaacd(8) is running and have even run it in debug mode with the -dv flags.

When I change the 'default router' statement in the rad.conf file to 'yes' on the first device and
restart rad(8), the second machine immediately picks up an autoconfigured address.

So my question is, is this expected behavior? When the router advertisement does not have a router and
thus sets the router lifetime to 0 (as it should), should slaacd ignore advertisement? Or should
it still configure an IP address?

I realize that this setup is not usual, so I'm just looking to confirm expected behavior.

Thanks in advance.