Reproduction steps:
1. Open the project from the attached file "1231188.zip"
2. Open the "GameObject" prefab
3. Right-click on GameObject in the Hierarchy go to XR and select UI Canvas
4. Select the newly created Canvas
5. Inspect the Event Camera field in the Inspector

Expected result: None(Camera) text is visible in the Event Camera field
Actual result: Scene mismatch (cross scene references not supported) text is visible in the Event Camera field

Reproducible with: XR 0.9.3-preview(2019.3.8f1, 2020.1.0b4, 2020.2.0a5), XR 0.0.6-preview(2019.3.8f1, 2020.1.0b4, 2020.2.0a5)
Could not test with: 2017.4.38f1(no package manager), 2018.4.20f1(XR Interaction package not available)

Notes:
- Not reproducible when adding a Unity UI Canvas
- XR UI Canvas is not added to the prefab