FTP connection from external source, showing up as firewall's DMZ interface

[jjj]

Our topology is this:

External Source > VPN Box > Web Filter Box > pfSense > FTP Server

When the external source connects to the FTP server, it can upload and download files just fine. However, the FTP Server shows the connection as coming from the pfSense's DMZ interface address. Any ideas how this could be?

In pfSense under the DMZ interface, I have "Disable the userland FTP-Proxy application" checked.

Thanks

[cmb]

The FTP proxy works that way, the proxy on WAN is what does that.

[jjj]

Why is it just for this topology? Clients connecting via the WAN interface show up with their normal IP.