iptables v1.2.6a (debian stable) doesn't seem to function correctly with kernel v2.4.24 if you're using the -m owner module. I used a backport from www.backports.org (http://www.backports.org/debian/dists/stable/iptables/) version 1.2.9 which seems to work fine.
the "MAC" listed when logging packets is the full MAC header, with the two MAC addresses and the Protocol (which explains their length).