Using IP aliases on a VLAN interface

[freebsd at jornane.me]

I'm trying to set up aliases on a VLAN interface.  My rc.conf looks
like this:

# /etc/rc.conf
vlans_igb0="vlan42"
create_args_vlan42="vlan 42"
ifconfig_igb0="up"
ifconfig_vlan42="inet6 2001:db8::42 prefixlen 64 mtu 1500"
ifconfig_vlan42_aliases="\
    inet6 fd00::dead:beef prefixlen 64 \
    inet6 2001:db8::babe:cafe prefixlen 128 \
"

However, after a reboot, a vlan42 interface shows up with only
2001:db8::42 as IP address.  The aliases do not show up, and any
services I've explicitly configured to listen on them fail to start.

After boot, I can run ipconfig to add the same aliases by hand, and
then everything works fine.  But I'd prefer a solution that works at
boot.

--
Jørn Åne