How to reproduce:
1. Open the attached project “22.2.12.zip“
2. Open the test scene
3. Select the 'Test' GameObject
4. Change the 'X' material field on Test Behaviour to a value e.g. Default-Diffuse in the Inspector window
5. Change the 'X' material field on Test Behaviour back to none
Expected result: X stays as “None”
Actual result: X stays as “Default-Diffuse”
Reproducible with: 2022.2.0a17, 2022.2.13f1, 2023.1.0b10, 2023.1.0a8
Not reproducible with: 2020.3.46f1, 2022.2.0a16