Windows firewall is only opening ports automatically for software when using UPNP, meaning, requests from your torrent client to the LOCAL router. It is not aware of this VPN end forwarding, meaning it's clueless that some port has been forwarded towards your computer. If you don't know how to enable a specific port manually (it's quite complicated, having to go through Control Panel -> Administrative Tools -> Windows Firewall -> Inbound Rules ; New Rule... and a whole bunch of clicking and stuff...) You might as well disable it when using VPN, since nobody can reach your computer ANYWAY, as you are behind that VPN server (which acts as the firewall !). That one will ONLY forward the specific ports you have configured in AirVPN interface, and none of the others.