802.1X on 3500yl and cisco phones

[stieven struyf]

my switches are configured with unauthenticated vlan 10 and no authenticated vlan->this is assigned by radius.
this works fine for pc's, but now i have a problem with cisco ip phones.
the ports i connect the phone to is authenticated and receives vlan 15 from radius.
The port also stays in "overriden vlan 10", so i the port is in 2 overriden vlan's at the same time.
On first boot the phone receives a good ip on vlan 15, but after it received its config it restarts and then it receives an ip on vlan 10.
Is this a known problem?