Vista - Problems with static ARP entries.....

I had a problem on our network with a server responding to ARP requests with
2 different MACs. That problem is now fixed as we added a different NIC and
disabled the onboard.

The problem above was casuing our Vista PC's not to communicate with the
server, so a call to MS had their Network Tech give us a work around of
adding a static entry to the Vista PC's for that server.

That worked great until we changed the server NIC's. I've deleted the
Static ARP entries with my Domain Admin account and with the users accounts.
The PC's will see the server for awhile then the static entry reappears with
the old address. So then they delete it and are good for awhile again.
Why does a static entry keep coming back?