Well, apparently the only servers you can see when you request for them on LAN are the ones that are using the default port 23073. Servers with custom ports won't be listed. (
Source).
So, you'll have to try and do it this way; Type the persons Ip into the Ip address field. If you don't know how to find out your Ip, go to Start -> Run -> Type 'Cmd' -> In the black box that comes up, type 'Ipconfig', or you can go
here. Then, click Join and hopefully you should join the game.
Please tell me if this works so I can add it as a solution to the Official Problems list.