Raised Terrain becomes distorted when using Raise or Lower Terrain Tool

Reproduction steps:
1. Open the attached “Terraintest.zip” project
2. Select Raise or Lower Terrain tool and draw across the Terrain GameObject in Scene window
3. Zoom in to the raised parts and observe

Expected result: Raised Terrain GameObject parts look smooth
Actual result: Raised Terrain GameObject parts have ridges

Reproducible with: 2020.3.43f1, 2021.3.15f1, 2022.2.2f1, 2023.1.0a24

Reproduced on: macOS Monterey 12.6 (Intel)

Note: Also reproducible in Build