Normally when you try to assign a key that is already bound, a warning appears indicating that the key is already bound to another action. This is not the case for certain actions in "vehicle movement". Specifically, "car fast forward" and "car slow forward" can be assigned the keys E and Q respectively, even though those keys are by default bound to "turn in" and "turn out" respectively. No warning appears that says the keys are already bound, it just lets them be.