Brush flickers when moving along with heightmap

Steps to repro:
1. Open attached or create a new project
2. Hierarchy > right click
3. 3D object > terrain
4. Select raise lower terrain from paint tab
5. Raise terrain's height
6. Move the brush along with height

Actual Result:
1. The brush keeps flickering, making hard to see what part is currently painted at

Expected Result:
2. Brush shouldn't flicker, when its moved along with the heightmap

Environment:
Windows and Mac

Occurring with:
2018.3.0a6, 2018.3.0a5, 2018.3.0a4

Note:
New Terrain tools are introduced from alpha 4

Working with:
2018.2.0f2