[Terrain] Artifact appears on a Terrain in scene view on attaching the “TerrainCopier” script.

When the “TerrainCopier” script is attached to the terrain, some Artifact appears on the terrain while painting in the scene view.

Steps to repro:
1.Create a new project.
2.Hierarchy > 3D object > Terrain
3.Attach "TerrainCopier.cs" script to the Terrain
4.Terrain > Zoom out > Paint terrain
5.Observe the Artifacts appearing on terrain

Actual Result:
Artifact appears on terrain

Expected Result:
Terrain is rendered without any artifacts.

Reproducible in:
2020.2.0b3, 2020.2.0b2

Note:
1. Unable to test on 2020.2.0b1, 2020.1, 2019.4, 2018.4 because of Bug ID 1152858
2. The issue is reproducible on macOS 10.15.2 and macOS 10.15.5 and unable to reproduce on macOS 10.15.1 and macOS 10.15

Environment:
macOS only