iptables ignores port 1900?

The following lines in iptables do not seem to work:

-A LOG-UDP-DROP -j LOG --log-prefix "IPT-UDP-DROP " --log-level debug
      --log-ip-options --log-uid
-A LOG-UDP-DROP -j DROP

...

-A OUT -p udp -d 239.255.255.250 --dport 1900 -j LOG-UDP-DROP

Packets described by the last line continue to pass my wifi,
and the indicated log line does not appear. Why?

Thanks,
Mike.