Port Check server not correctly configured

[Edified]

Just FYI, if you're having trouble getting a peer listening port open and you have a WebProxy...
-I'm running NAT on a MicroTik RB450G with port forwarding correctly configured.
-Transmission reports that the specified listening port is CLOSED
- http://www.whatsmyip.org/port-scanner/ reports that it's OPEN, also correctly reporting that other ports are closed.
- Established connections are listed on the RB450G with the DST WAN address and the peer listening port.
-When I disable port forwarding on the RB450G whatsmyip correctly reports the port closed and no new connections appear on the router.

I have MikroTik's WebProxy running with a parent Squid Cache. They are running only on port 80. If I disable the proxy the port is correctly reported OPEN by Transmission. When the proxy is enabled, Transmission reports "Port is Closed".

Something port check system that sometimes causes it to falsely report "Port is Closed" when it is actually open when a web proxy is used. It could be a HTTP header that includes the local address, which would cause Port Check to look for an open port on a private network address.

I don't know if your port check server keeps logs but check it for 10.0.7.7 Port 3900.

Or does someone else have another idea?

[Edified]

And that would be the X-Forwarded-For header.

The Transmission Port Check server is configured incorrectly for cases where a proxy is in a private subnet and adds a X-Forwarded-For header.

The port check server should check if the X-Forwarded-For http header is a private address and if it is it should Port Check the public WAN address rather than the X-Forwarded-For address.

Not a flaw in Transmission per se but a flaw in a supporting service.