Discovered an interesting problem with windows xp and 7 clients in an active directory domain(although this may happen to non-ad clients as well). If the dhcp server has several different DNS servers for different groups of clients, and a default is overridden by the others, the override doesn’t go into affect when a lease is acquired on reboot (only a manual renewal seems to get it).
The fix was to set up the dns options so that no “default” existed (i.e. the other groups each got the same entry placed inside a subgroup for them). Then both the windows and other clients picked up their own dns options with no overrides.
Essentially, what I did was move
option domain-name-servers 192.168.2.1
into
group ( ),
so that no default exists.