1) Check to be sure that you're using static addresses, not DHCP.
2) Check to see how many NICs are active on the host. Remove/disable those that are not needed.
3) Find out what 85.255.x.y is. This will perhaps offer a clue as to why the host is grabbing this address.
4) Was this box on that 85 network before? If so, find out what it was used for and clean out all the settings associated with that network.

--Th13