[syslog-ng]Question regarding syslog-ng filter

I'm using syslog-ng 1.6rc4 Can anyone tell me what is wrong with this filter: filter f_kern { facility(kern) and (not match("IPTABLES DROP") or not match("New not SYN:")); }; I still can see lines with IPTABLES DROP in my kernel log:-( Why these messages still come through this filter? Thanks. What am I missing?