How to reproduce:
1. Create a new project
2. In the Inspector, click the hamburger menu icon at the top-right of the window and select Add tab > Inspector
3. In the Hierarchy, create a Terrain GameObject
4. Select the Terrain GameObject
5. Activate the first Inspector by selecting it, and press "Activate this inspector"
6. Change the brush size
7. Click anywhere in the Scene View to deselect the Terrain
8. Select the Terrain again
9. "Activate this inspector" in the Inspector again, and observe the value

Expected result: The brush value remains what it was set to in step 6
Actual result: The brush value resets to a previous value (before step 6)

Reproducible in: 6000.0.7f1 (7dd95c051e11), 6000.0.59f1, 6000.2.7f1, 6000.3.0b4, 6000.4.0a1
Not reproducible in: 6000.0.6f1

Reproduced on: Windows 11 Pro (24H2)
Not reproduced on: No other environment tested

Notes:
- In 6000.0.6f1, the Inspector does not provide the “Activate this inspector“ button, and it looks like all Inspectors are active at any moment, the change to introduce it likely introduced this
- In some versions, the Paint Terrain tool gets deselected, if that happens, just select the second tool in the Inspector (“Paint Terrain”) before step 6