Xbox360のコントローラが公式ドライバだとDirectInputでトリガーが1軸になってるとかは、
過去のゲームとの互換性のためにあえてそうなってるだけで、不具合とは言わないよ。

> The combination of the left and right triggers in DirectInput is by design.
> Games have always assumed that DirectInput device axes are centered when there is no user interaction with the device.
> However, the Xbox 360 controller was designed to register minimum value, not center, when the triggers are not being held.
> Older games would therefore assume user interaction.
> The solution was to combine the triggers, setting one trigger to a positive direction and the other to a negative direction, so no user interaction is indicative to DirectInput of the 'control' being at center.
> In order to test the trigger values separately, you must use XInput.