Firebox III/500 ARP problem

[Dredd123]

Hi,

One of our customers Watchguard firewalls appears to be responding to ARP broadcasts with it's own MAC address on the trusted network. This is causing major problems on the LAN. I am not familiar with Watchguard kit at all, so does anyone know why this is happening (proxy ARP?) and how to turn it off (if turning it off is the right solution)?
P.S. Please see the ARP table from the Firebox included below. All the ARP mappings with flags of CMP contain the MAC address of the trusted interface of the Watchguard.

Thanks,
D.

ARP Table:
Address HWtype HWaddress Flags Mask Iface
192.168.1.240 ether 00:50:7F:26:F7:FF C eth1
195.74.99.193 ether 00:20:6F:18E:46 C eth0
192.168.1.178 ether 00:0F:1F:0F8:5A C eth1
192.168.1.5 ether 00:07:85:A2:C9:29 C eth1
192.168.1.10 ether 00:0BB:A9:52:A7 C eth1
192.168.1.172 ether 00:48:54:50:12:0B C eth1
192.168.1.201 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.203 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.186 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.194 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.196 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.202 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.192 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.191 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.189 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.195 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.190 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.181 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.183 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.184 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.188 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.197 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.182 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.187 ether 00:90:7F:20:90:15 CMP eth1
192.168.1.185 ether 00:90:7F:20:90:15 CMP eth1