my car does the same thing, the key will come out with no effort at all. i did get myself a new key that is tighter but also will come out.

so im thinking its the lock tumbler. what i do is when i shut my car off to park it. i make sure the ignition is locked after the key is out. or you can have a dead battery in the morning.

if the key does come out while driving, ( even a little bit) my security light comes on, but the car still runs fine for me.