Open Port 80 not found by Firewall Test

This is my first post. I hope this is in the right place.

I have been using the AuditMyPC firewall scanner and have both kudos and a grumble.

The "Standard Security Scan" found an open Port 4567 which turned out to be a deliberate backdoor in my Actiontec modem. I have been able to close that one – thank you.

However…… I am running a web server on Port 80 and none of the available scan modes (Standard, Ranged or Advanced) seems to be able to find it.

I’ve tried GRC’s Shields Up and NMap. Both respond appropriately as I start and stop my WWW server.

What’s up?