I too had a similar problem. I forced the ip address to be my cable modem port and I was not getting and inbound connections. I verified this with:
1. netstat on the local machine - local addresses never had 6346 and established.
2. tethereal on the masq machine and watching the syn and fin packets.
3. Connecting from the outside with a modem and nmap'ing my site and finding 6346 as closed.

I unchecked forced and all of the above tests indicated that inbound connections were working.

HTH
bob

p.s. is there a better forum to talk about tech stuff? like a ng.