Basically, while you can assign the Xbox 360 controller to any controls you create, the only ones it actually works with are the default controls assigned by a behavior-- for instance, Up, Down, Left and Right. If you add an extra control, like a "Fire" button, and detect it using events, nothing happens. This also applies to detecting extra presses of Up, Down, Left and Right-- they won't be seen either.
Example is attached. Keyboard controls-- Arrows move, control spawns a green box. The 360 controls are mapped so that A also equals the fire key and should spawn a green box when it is pressed, however, it does not.
This also affects third party plugins like CustomControls, which has the exact same issue.
360 Controller Bug