Reproduction steps:
1. Open the attached "repro_IN-84102" project
2. Open the "Assets/OutdoorsScene.unity" Scene
3. Open the Scene view
4. Turn around until both sides of the terrain is neatly in front of you
5. Press on the left part of the terrain
6. In the Inspector, the "Terrain" Component, press the "Paint Terrain" button and select "Paint Texture" in the dropdown below
7. In the Inspector, the "Terrain" Component, under the "Terrain Layers", select "New Layer 1"
8. Press the right mouse button on the "Hierarchy" tab and select "Add tab -> Inspector"
9. In the Scene view, paint a line that starts on the left part of the terrain and goes into the right part of the terrain
10. Observe the "Terrain" Component in the Inspector on the right

Expected result: The "Terrain" Component values stay the same
Actual result: The "Terrain" Component values resets

Reproducible with: 6000.0.7f1, 6000.0.20f1
Not reproducible with: 2021.3.44f1, 2022.3.47f1, 6000.0.6f1

Reproducible on: Windows 10 (22H2), Windows 11 (10.0.22631) (user's)
Not reproducible on: No other environments tested

Note: Sometimes, the “Terrain“ Component values reset with only one Inspector open, but this reproduction method is inconsistent