Been playing with this a bit and it's actually a can't-win situation: If you change DHCP from disabled to Automatic then the *&#$*# AP starts assigning IP addresses to (some) connected devices...

@mocelet: Nice piece of detective work! This same TP-Link bug also affects the WA1201, and from reading the huge thread here it looks like it's endemic to all TP-Link products, if you disable DHCP...