Windows XP and EAP-logoff

Hi, I working on dynamic VLan assignement using FreeRadius, and I'm trying to authenticate machines before the users. When the machine starts, it uses its own credentials to access the network, then the user logs on using the Windows XP GINA. My problem is that the user, after that, is still accessing the network with the machine account. It's only when I manually unplug and re-plug the Ethernet cable that the user uses its credentials I've tried setting the AuthMode to 1 and the SupplicantMode to 3, as advised, but it's still not doing an EAP logoff when the user logs on. Am I missing something ? -- GPG key : 0xC417137E