From GitHub: https://github.com/Unity-Technologies/InputSystem/issues/384

Repro:
1. Download package and project at: https://github.com/Unity-Technologies/InputSystem/issues/384
2. Open SimpleDemo scene at: Assets -> Demo -> SimpleDemo
3. Find "Player" gameobject in the Hierarchy window and select it
4. Find the attached script "SimpleController_UsingActions_InAsset" on the object
5. Find "Controls" field and click the round dot next to the input field
6. Observe the options provided

Actual: Though in the script, "Controls" is set to be SimpleControl, all InputActionAssetReference show up.