How to reproduce:
1. Create a new project
2. Open the “SampleScene”
3. Add the Terrain GameObject to the Hierarchy (3D Object → Terrain)
4. Create a Prefab in the Assets folder (Assets → Create → Prefab)
5. Open the created Prefab
6. Add the Terrain GameObject into the Prefab
7. Paint the Terrain by using Brush in the Paint Terrain tool
8. Close the Prefab
9. Observe the Terrain in the “SampleScene”

Expected result: The Terrain GameObject remains unedited
Actual result: Changes applied to the Terrain in the Prefab are reflected on the Terrain GameObject

Reproducible in: 2021.3.37f1, 2022.3.24f1, 2023.2.18f1, 6000.0.0b14

Reproduced on: Windows 10
Not reproduced on: No other environments tested

Note: reproduction depends on the Brushes used:
- Always reproducible with builtin_brush_12 and builtin_brush_2
- Not reproducible with the builtin_brush_1
- Inconsistent reproduction with other Brushes
- Only some parts of the changes are transferred most of the time