Inbound port forwarding redux

I would really appreciate some input on this problem!

My old Linksys router died, so I got a new one. However, I am unable to get inbound port forwarding to work on this one. You can see my settings and there's not much that can be wrong.

One day by accident I stumbled upon a clue: it seemed as if the connection started, and then died immediately. This didn't produce any new insights, nor did anyone suggest any new ideas in response to the blog post.

I had two services being forwarded; port 81 to HomeSeer, and port 22 to SSH on my Linux box. Neither worked. I had an idea this morning and set up a third, on port 5555, running to a MUD I have on the Linux box (for development purposes; I don't actually host a MUD... obviously, since my port forwarding doesn't work). Then from work I tried to connect to it, and it connected long enough for zMUD to say "Connected to host tricklebrook.dyndns.org", but then I never saw the login screen. Subsequent attempts to connect didn't even get that far. Same as the web logon, really.

So it is establishing the connection, but it only lasts a few seconds. Does that suggest anything?