arp rejecting not working

[budsz]

Hello,

I've strange problem in FreeBSD 8.0-STABLE:

root:~# uname -smr
FreeBSD 8.0-STABLE i386

root:~# arp -a | grep pcbill
pcbill.domain.net (192.168.100.100) at 00:1c:f0:63:03:08 on rl0
permanent [ethernet]

root:~# arp -s pcbill.domain.net 00:1c:f0:63:03:08 reject

root:~# ping 192.168.100.100
PING 192.168.100.100 (192.168.100.100): 56 data bytes
64 bytes from 192.168.100.100: icmp_seq=0 ttl=128 time=218.360 ms
64 bytes from 192.168.100.100: icmp_seq=1 ttl=128 time=14.318 ms
^C
--- 192.168.100.100 ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 14.318/116.339/218.360/102.021 ms

But on other machine:

root:~# uname -smr
FreeBSD 7.3-STABLE i386

root:~# arp -a | grep mdm-po-02
ip.mdm-po-02.p2m.domain.net (10.2.0.1) at 94:0c:6d:be:9e:1a on rl3
permanent [ethernet]

root:~# arp -s ip.mdm-po-02.p2m.domain.net 94:0c:6d:be:9e:1a reject

root:~# ping 10.2.0.1
PING 10.2.0.1 (10.2.0.1): 56 data bytes
ping: sendto: Host is down
^C
--- 10.2.0.1 ping statistics ---
1 packets transmitted, 0 packets received, 100.0% packet loss

Any change log or something in FreeBSD 8.0-STABLE about arp -s command?

Thanks in advance.

-- 
budsz