ipfw and MAC Addresses

[traore at afribone.net.gn]

I'm using Freebsd 5.0 Release.
And i want to use ipfw with Mac adresses fitering. But its not working.
When i add a rule like:
ipfw add 49 deny mac any 00:E0:18:F1:57:94 

the kernel change it to be:
ipfw add 49 deny ip from any to any mac any 00:E0:18:F1:54:94 

Can you help me?

Rgards!