Activesync overwrites DeviceID

I have a customer that syncs multiple WM50 MC70 devices to his PC using Activesync.  Each device was given a unique DeviceID under Settings>SystemInfo>DeviceID.  When he syncs a device, ActiveSync renames the DeviceID to that of another device that has been previously sync'ed.  Can someone tell me how to stop this? 

Thanks,

Clayton