Web access from WAM not working?

[cjin]

I'm running 476.45 on N66U, have web access from WAN enabled (port 8080, not restricted to specific IP)

When I tried to access router from iPhone on port 8080 (thru cellular), it couldn't connect.

If I forward port 8181 to local IP of router on port 80, then I was able to access router from iPhone on port 8181.

Is this a known issue? What should I check?

Thanks