WiFi active while in Airplane mode and Carrier Automatic switch wont stay off

I have two identical iPhone 3GSs. Both are locked to the Canadian Rogers network and are not jail broken. They are both running iOS 5.1.

One will not activate WiFi when in Airplane mode, and maintains the Carriers->Automatic in the OFF position. The second phone wil allow the WiFi to be activated in airplane mode and activates itself on foreign networks. If I turn the Carriers->Automatic to the off position and then carry on with using the phone it will try to activate a foreign cellular network. When I return to Carriers->Automatic the switch has returned to the ON position.

As far as I can tell the two phones should be identical, any idea what is happening with the second phone?

Thanks