HPNA power line adapters shouldn't make a difference. Port forwarding is based on LAN IP address, and if your router doesn't agree what your local IP is then port forwarding would be the least of your problems. Some routers can do port forwarding based on device name, but again, the adapters shouldn't make any difference there.
The only way I could see a problem is if you're forwarding ports based on MAC address, and the router is seeing the MAC address of the first adapter instead of your PC (or whatever it is)? In that case, I'd suggest either finding the MAC of the adapter and forwarding to that, or switch to forwarding based on static IPs. That shouldn't happen with most adapters though.
Another possible scenario: If you were using WiFi before, you might still be trying to forward to the IP or MAC of your wireless card instead of your Ethernet card.
That's all I can think of. I've used multiple combinations of different brands of adapter with tons of different routers, PCs, and game consoles. Never had an issue with port forwarding. I hope you can find a fix.