Unfortunately it's not that simple. The reason they don't re-query the mac address is because they have it cached locally. They way to fix this problem is as root on each run an 'arp -d' (since very few machines will 'listen' to an unsolicted ARP broadcast)
Or as an alternative, it's possible (certainly on solaris) to re-configure a mac address on a card. You 'backup' server would then be able to steal the mac of the master server.
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It's not pessimism if there is a worse option, it's not paranoia when they are and it's not cynicism when you're right.