How to reproduce:
1. Open the user's attached project
2. Open the 'SampleScene'
3. In the Probuilder toolbar select 'Face Selection'
4. In the Scene select the green face of the Cube
5. In the Probuilder window select 'Detach Faces'
6. Observe the Cube
7. Undo the changes
8. Select the red face of the Cube
9. In the Probuilder window select 'Detach Faces'
10. Observe the Cube

Expected result: The faces remain the same
Actual result: When the green face gets detached the whole Cube turns green, when the red face gets detached the selected face turns green

Reproducible with: Probuilder 5.0.3 (2019.4.26f1, 2020.2.7f1, 2021.1.7f1, 2021.2.0a16)
Not reproducible with: Probuilder 5.0.1 (2019.4.26f1, 2020.2.7f1, 2020.3.8f1)
Cannot test with: Probuilder 5.0.1, 5.0.3 (2018.4.35f1) (the package versions are not supported)

Notes:
- After performing step 7 in 2021.2.0a16 part of the faces disappear