Wireless EAP - GPO Problem

I having an interesting problem and hope someone can help.

Windows Vista client machines:

I have configured the wireless GPO. Wireless network is configured with
802.1x with IAS and using EAP for authentication. The GPO is set for
"computer authentication" so the laptops authenticate prior to the user
logging in. This alleviates the problem with users having to log in first
with a network cable attached.

Also - I have disabled cached logons in the GPO because I really don't want
users logging in if the network is down. I also disabled power save on the
wireless NIC. It does not turn off if the computer goes to sleep.

The laptops work perfectly for a time then seem to randomly lose the GPO
settings. I then have to plug in the network cable, login and reboot. After
the reboot everything seems fine for awhile.

Any tips or thoughts? Thank in advance!
Nick