d458273 created the issue

To reproduce:

1. Using Cyberduck 6.9.4 on Mac OSX (I am using 10.14.4) define an FTP connection with this parameters https://i.imgur.com/ILpx6h0.png (notice the 'Use browser connection' and 'PASV' settings)

2. Setup a network sniffer to view the cyberduck traffic (I am using Wireshark)

3. Establish the ftp connection and open a directory with a file.

4. Initiate a Download operation and view the captured packets in the network sniffer.

Expected: Cyberduck use the existing FTP control connection to initiate a PASV file transfer (as it does when opening a sub directory in the FTP browser)

Actual: Cyberduck tries to open a new command connection at the host FTP port (viewed as a SYNC packet).

Impact: this prevents using Cyberduck with network appliances that are limited to a single FTP connection. FileZilla on the other hand works as expected with those appliances.