Multipath rules and proxied FTP traffic

Hi,

I have two internet connection and set up the following 3 multipath rules:
Internal --> WebSurfing HTTP(S) --> Any --> Connection 1
Internal --> FTP --> Any --> Connection 1
Any --> Any --> Any --> Connection 2

So I want to use Connection 1 only for surfing traffic and downloads and Connection 2 for the rest.

The web traffic is handelt by the internal web protection proxy with is working well with the multipath rules.
FTP is also used via the web proxy, no separate ftp proxy or firewall rule active but here the multipath rule seems to be ignored and FTP traffic passes Connection 2.

What am I doing wrong? Any hints?

Thanks,
Stephan