Details are not being painted according to the selected brush

Steps to repro:
1. Open attached or create a new project
2. Hierarchy > right click
3. 3D object > terrain
4. Select paint details from tab
5. Edit details > add detail mesh or grass texture
6. Select star brush or any other brush and paint

Actual Result:
1. Detail meshes are being painted as square irrespective of the selected brush

Expected Result:
1. Details should be painted according to the selected brush

Occurring with:
2018.3.0a8

Working with:
2018.3.0a7, 2018.3.0a4

Note:
New Terrain tools are introduced from alpha 4

Environment:
Windows and Mac