I have the same problem.
I've opened up some ports that I wish to use in the advanced settings then under port fowarding under firewall.
I've set the ports I want to open up and assigned it to the devices ip address from the drop down list. However when I do a port scan it doesn't show that the port is open. I have rebooted the router and that made no difference.
Also what I noticed when I try to ping my real world IP address the pings are unsuccessful. I disabled the firewall on the HH5 but again no difference.
I am using BT Home Hub 5 - Software version 184.108.40.206.83.8.204 (Type A).
Really confused. Any help would be appreciated as I cannot access some devices from outside the network.