For me, it works (for more than one forwardings) like OP posted but I needed only the setting he described in "Advanced -> NAT -> Virtual Server". I assume that your WAN1 is connected to a dumb ADSL...

A Class B private address space (instead of class C now) should help: https://en.wikipedia.org/wiki/Private_network Or add VLAN, have more than one DHCP server and different LAN-subnets.

Might be that the detection uses a DNS server to ping it for the test. Maybe your provider did not provide a pingable DNS via DHCP? Try to set Google DNS 8.8.8.8 / 8.8.4.4 for the WANs instead?

I am in contact with German support in Germany (yes that exists!) and I have the same issue (TL-R470T+ V4). I'm testing right now (FW 1.1.0) but it seems to be connected to DynDNS services switched...