To reproduce:
1. Open the project “BugTesting”
2. Select “SPUndo” GameObject in the Hierarchy
3. Click the ““ button in the Inspector
4. Select any other GameObject in the Hierarchy
5. Select “SPUndo” GameObject in the Hierarchy
6. Click “” and “-” in the Inspector and note how the bar is changing its color
7. Click the “-” button in the Inspector
8. Select any other GameObject in the Hierarchy
9. Select “SPUndo” GameObject in the Hierarchy
10. Click “+” and “-” in the Inspector

Expected result: The bar is changing its color like in the 6th step
Actual result: The bar remains green

Reproducible with: 2022.1.16f1, 2022.2.0a12
Not reproducible with: 2022.2.0a13, 2022.2.0b7, 2023.1.0a10
Could not test with: 2020.3.39f1 (Console errors), 2021.3.9f1 (Warning*)

Reproduced on: macOS Monterey 12.5.1 (Intel)

Notes:
- The script is at Assets → SerializedPropertyUndo → Editor
- 2021.3.9f1 Warning “Binding is not supported for managedReference<SPUndoSubclass> properties "reference"“