we have the problem that after almost 30min logged out win7 computers (HP probook 640, Dell Latitude 6420 both with the latest BIOS) the McAfee (PBA) login screen (PIN) disappears and only a hard reboot helps. This happens only if the smart card is in the card reader - isn't it, then the login screen is available.
Given that EEPC6 is only supported for the next 5 days, the best thing to do would be to upgrade to the current version of MDE and see if the problem can still be reproduced.
My gut feeling is most likely the internal smart card reader is powering down. Seems an odd situation though - to leave a machine at the pre-boot screen without powering it off or logging in?