Multiple Machine IDs (repeatedly)

Hi,
I am running boinc on a bunch of desktops with different O/Ss and capabilities. We had a storm which
took out the power and then yesterday we had another power outage. After these, it seems that all of my
machines bar 1 XP box have created new machine IDs.
Is there some issue with crashes causing the machine/user IDs to be lost ?
This has happened with solaris, linux and a Win2k
client. The only difference I can see between these and the XP box (which works OK) is that XP has been shut down cleanly since I started running BOINC.