How to reproduce:
1. Open the attached project "1209514.zip"
2. Select Cube GameObject in the Hierarchy window
3. Observe the Inspector window

Actual result: In the Inspector window there is a light gray line visible in the header for the GameObject and for the Material
Expected result: There is no light gray line(s) visible in any part of the Inspector window

Reproducible with: 2019.3.0a9 (Entities preview.31 - 0.0.12, preview - 0.1.1), 2019.3.0f4 (Entities preview - 0.1.0, preview.10 - 0.4.0) 2020.1.0a19 (Entities preview - 0.1.0, preview.10 - 0.4.0)
Not reproducible with: 2018.4.15f1 (Entities preview.24 - 0.0.12), 2019.2.18f1 (Entities preview - 0.1.1), 2019.3.0a8 (Entities preview.2 0.0.12, preview - 0.1.1)
Could not test with: 2017.4.36f1 (Entities package was not introduced)

Note: After installing Entities package, sometimes it requires a Unity Editor restart in order to see the visual bug