Is it possible that it is just getting triggered by something pressing the power button, then something else hitting the airplane mode on-screen or with optical pad?
I know that if you bring up the power button menu once (called phone options) , it will stay on unless you hit the back button to bring up the unlock screen. Even if you hit the button again to kill the screen the next time you hit the end/power button that menu always pops back up.
With this menu always on screen the chances of something else enabling airplane mode, are much higher. Even if it is not enabled vis touchscreen, it can be enabled via the optical pad.
Is it possible that enabling airplane mode just once (even if the user was unaware that it happened), causes the phone to always go back into airplane mode due to a bug/glitch?