John, what is in you picture is in fact the "range port forwarding" and not the "single port forwarding". This "single pf" seems to be a new feature. It is in my WAG, but it is not in my WRT (much more stable, I have to say). In the Single PF, you can forward single "eternal" ports to (different, but not necessarily) "internal" ports.

For example, if the WAG receives a request on port 80 it can forward it to port 8080 on any internal server. Of course, you may specify the same "external" and "internal" port (80->80). Port ranges are not supported.

The point is that this feature is malfunctioning, and will stop forwariding at some point, apparently in a random fashion.

I am now using the Range Port Frowarding and all seems to be going well. So far.