GitHub: https://github.com/Unity-Technologies/InputSystem/issues/539

Repro:
1. Download package and project at: https://github.com/Unity-Technologies/InputSystem
2. Open Input Test scene at: Assets -> QA -> Input_Test -> Scenes -> 02_Input
3. Make sure in Player settings, Input Handling is set to "Input System (preview)"
4. Enter Playmode
5. In the Keyboard and Mouse test, press Ctrl + i to see the input information
6. Move and scroll mouse and observe the value change for old system

Actual: The old Input System still detects mouse position and scroll when only the new ISX is used as Input Handling.