The port indexes in OpenWRT and in hardware (on the case) are swapped:
Port index in /etc/config/network
CPU 0
1 4
2 3
3 2
4 1
It is possible to run 802.1Q tags on these ports. As of Chaos Calmer mixed (tagged/untagged) VLANs are working, and can be configured via LUCI. The maximum VLAN number is 15.