ftp-proxy, PF not working with FTP traffic

Hi there.
Im running freebsd 5.X with a pf firewall doing NAT, so as all the 
manuals said I setup the ftp-proxy to allow ftp clients behind the PF 
NAT connect to external FTPs server,  but the way this work all the data 
traffic coming back when I running an ftp connection on active mode, it 
is coming back with the IP number of my  freebsd box, some windows 
client doesn't care about it, but Mac os users or NCFTP drop the 
connections when this is happening.
I tried all the possibles options on ftp-proxy and all the version 
possibles with the same end.

somebody know how fix this, or if it another option to make work ftp 
clients no PF?

thanks
Marcos