Hi
I also got the message about the port changing, but it didn't appear to change under the management page. I could still access the routers admin page on port 80 fine internally, it might just make the change for connections from the WAN.
There is another way to add to a web server, under NAT go to Applications, Add new application, select the WAN interface required, then the internal server IP address to forward to, for Application Category select Servers, and under Application Forwarded select Web Server and OK.
This sets up ports 80 and 443, of course you may not need port 443 forwarded but it's done all the same and does no harm.
There are quite a few applications than can be added if required, I've also added PPTP.
A tip, if there is any chance you are going to change from using VDSL on the router to the it's WAN Ethernet or vice versa, then set up another Application for the Web server from the alternative port. That way if swapping it will still work without needing any config changes.
I've noticed under Port Forwarding they have the label "Trigger Start Port:", this is wrong, and initially got me confused thinking it was Port Triggering and not forwarding I was setting up, it should of course say "Translation Start Port:".
Regards
Phil