How does a ftp-server log real ip-address of client machine?

Wed Dec 29 21:12:36 UTC 2010

I usually connect to my servers through the Tor.
When I connecting with them through ssh or sffp I don't find any serious
in logs of my server except ip--addresses or names of apropriate
exit-nodes of the Tor.
But when I connect with them through ftp immediate (without ssh) I can
see real ip-addresses of my client's machine such the next:
proftpd[32816] someuser (anonymizer2.torservers.net[174.36.199.200]):
Refused PORT 192,168,1,5,203,191 (address mismatch)
As I understand if my machine would not be behind NAT and have 'white'
ip-address my anonimity would be compromised.
How does a ftp-server log real ip-address of client machine? And how I
can avoid it?
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