Repro Steps:
1. Create a Terrain Object
2. Paint some hills onto the Terrain object
3. Zoom in a bit on the Terrain and get a view that is decently well lit
4. Select the Terrain Object
5. Select the Terrain Settings Tab
6. Scroll down to "Heightmap Resolution" and change it from 513 x 513 to 4097 x 4097

Actual Results:
Observe the Terrain will appear more "lumpy" than before

Expected Results:
The Terrain object would look the same as it previously did, if not then even smoother than before due to the resolution increase.

Note:
Terrain Tools package was installed during my reproduction of this case