Setup wizard breaks single interface configurations
After going through the setup wizard with a single interface assigned, you're left with a broken configuration. LAN is added to the config as this:
<lan> <ipaddr/> <subnet>1</subnet> </lan>
Which drops LAN into the firewall ruleset even though it isn't assigned to an interface, breaking the ruleset amongst other things.
Likely best resolution: if only one interface is assigned, skip the LAN configuration page.