Forwarding Port 80 triggers Router Detection alert on 3801HGV

I looked around in this forum and didn't see reference to this, so here goes:

I am trying to forward port 80 to a Mac server. I already forward 22 to a NAS and that works fine.
 However, after setting up the computer in the web interface with the forward it seems to work until I access it in a browser. This seems to trigger some kind of circular reference that causes the 3801HGV to think I have another router on my network, which I don't.

So, my questions:

Can the router detection be turned off? It intercepts all my http traffic and effectively kills web traffic on my network until I reset the device information on the 3801HGV.

If I can't turn it off, is there another way to set up forwarding of port 80?

I should also say that I did try this with a router, and set it up as a router on the 3801HGV but I couldn't access the internet though the added router.

Thanks in advance for any tips. This forum is a great resource.