What is the port you want yo open? How are the devices are connected to the router?What are the setting you have done on the router? What is the IP address for the WAN on Archer C7? How did you test the port is opened or not? In my network, i am using the latest firmware 130617 .Here are my network environment: Internet---WAN 4300 LAN---HFS（port 8000），open port 8000 on WDR4300.
try to access http://wan IP:8000, succeed.

my bad,:D solved, it was wrong ip for port forwarding on DSL modem,
Now after I redacted this post to reply to you, and read it for mistakes
"like I said before this update port forwarding was working OK, now no matter what port I choose is the same result from on MAC and on PC, both connected via wireless to tp link 4300

my home network consist in 1 DSL modem, 1 router (4300) connected via cable to the DSL modem and a bunch of phones and computers connected wireless to the 4300 router on encrypted connections, all configurated without DHCP, only manual IP on all clients. I filtered mac on security panel on wireless security, all my clients are binded to the 4300.

I have port forwarding configurated to DSL modem on port 65535 for router (4300) IP, and on router I have port forwarding for same port but for a client computer IP.

When I made the update for 4300 I do not go with reset first. I possible to be a bug from previous settings on new firmware ? a light came to me.:p