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"“