How to reproduce:
1. Open the attached "UnityMR_Validation.zip" project
2. Open the "UnifiedInputTest_Scene" scene
3. Enter the Play mode with the attached VR headset and controllers
4. Press different controller buttons and observe the UI in the scene

Expected result: While pressing the controller buttons, correct buttons are logged in the scene UI.
Actual result: While pressing the controller buttons, incorrect button mapping is logged (e.g. Trigger press is treated as ThumbstickPress)

Reproducible with - 2018.2.0b1, 2018.2.0f2, 2018.2.5f1, 2018.3.0a9
Not reproducible with - 2017.4.14f1, 2018.1.9f2, 2018.2.6f1, 2018.2.14f1, 2018.3.0a10, 2018.3.0b8, 2019.1.0a7

Note: When pressing the controller button on versions in which the issue is present, "XRInputDeviceState: Failed to set the value at featureIndex [4]." errors are thrown in the Console window.

Fixed in 2018.3.0a10
Backported to 2018.2.6f1