Yeah, it's working as designed.

The firewall area and the 'Force IP' checkbox is just telling LimeWire, "Hey, advertise my IP & Port as something other than what I think it is." LimeWire will automatically determine the IP (based on Remote-IP headers), but needs you to tell it the port. The port value here is not what it's actually listening on, but what the outside world thinks it's listening on (so that you could, for example, have the a router forward connections to port 6700 to your computer's 6346 port -- LimeWire needs to tell outsiders it's listening to 6700).

The port area is for telling LimeWire to open up a new listening socket on a different port.