FTPES behind NAT uses internal address

[rotorman]

I have posted this post before, now posting it with debug logs as required.

Using FileZilla 3.0.0-beta5, connecting to Synology DS-106 (192.168.77.8), with FTP-SSL support. DSL router has port forwarding on external 21->internal 21 and passiv port range 55536-56559 to internal configured.

All runs fine in LAN (FTP and FTPES connections).

When connecting with FTPES from WAN to a "misconfigured" FTP server behind a NAT that reports its internal address, the connection uses PASV(internal IP,PORT) even if under Settings -> Connection -> Passive mode the radio box is on "Use the server's external IP address instead".

Connection works with plain FTP over WAN (in this case FileZilla uses correctly the external address - the address of NAT box), all goes unfortunately plain-text over the network this wan :(

Attached are 3 logs in ASCII (zipped as one file).
Log1 - LAN FTPES, success
Log2 - WAN FTPES, failure by LIST
Log3 - WAN FTP, success

[rotorman]

Debug Logs (3), FTPES LAN, FTPES WAN (failure), FTP WAN

[Tim Kosse]

Command: PASV
Response: 227 Entering Passive Mode (192,168,77,8,220,58)
Trace: Server sent passive reply with unroutable address. Using server address instead.
Command: LIST
Error: Connection timed out

Misconfigured server. According to the logs, FileZilla properly falls back to the external IP address. Try using active mode or contact the server administrator.