I'm not sure what it is, but I got the same misbehaviour when everything was connected via hubs instead of the newer 16-way switch.

Just for kicks, I have one of those $5 router/gateway boxes here, with a built-in DHCP server. I'm going to plug that into the switch and see if the empegs are any happier. If it works, then perhaps a software upgrade to the latest DHCPD sources may help.

Cheers