The assigned texture doesn't scale properly when Inspector window shrinks horizontally

Steps to repro:
1. 1. Open attached or create a new project
2. Hierarchy > right click
3. 3D object > terrain
4. Select paint texture from paint tab
5. Edit terrain layer > Add a layer
6. Create a layer and assign a texture to it
7. Click on Add layer to add it to terrain
8. Darg Inspector window horizontally

Actual Result:
The texture doesn't scale and its selection box is visible when Inspector window shrinks horizontally

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

Environment:
Windows and Mac