After upgrade to Zimbra 6.0.5 we've got a problem with forwarding messages matching the filter's conditions of mailbox.
Example:
I have address first@mydomain.com with alias second@mydomain.com.
The filter is configured to forward messages with To = second@mydomain.com to another address myfriend@mydomain.com.
Everything works perfectly except myfriend@mydomain.com gets mail with header "From:" set to first@mydomain.com. And address of original sender gets lost forever.