Materials can not be modified when using ScriptedImporter

Reproduction steps:

1. Open the attached project (“Bug.zip“)
2. Select Assets/NewMat
3. In the Inspector window check “Set Keyword” checkbox
4. Click apply button
5. Observe the color of the “NewMat” material

Expected results: The color of the material changes to green
Actual results: The color of the material stays red

Reproducible with: 2020.3.37f1, 2021.3.6f1, 2022.1.10f1, 2022.2.0b2, 2023.1.0a2

Reproducible on: Windows 11