Issue with NATed ports of a Firewall?

The Evostreamer is set-up with the ports 1935, 8443 and 8080 for rtmp, rtmps and rtmpt. The outside world gains access through a NATed firewall. outside 1935 –> inside 1935 outside 80 –> inside 8080 outside 443 –> inside 8443 With a simple telnet check: connections inside the machine to the ports are possible connection from outside to port 1935 is establishable connections to port 80 and 443 from outside is not possible. (I cross checked the firewall rules and took another application listening of port 8080 and 8443 and everything is fine). Therefore my question: Does Evo do a double check of incoming packets and on which port? If the incoming number 80 and the real number 8080 do not fit, the packet is dropped? How can I overcome this issue?