Properties become unusable and their input field distorts when "Import Heightmap" window shrinks horizontally and vertically

Steps to Repor:
1. Open attached or create a new project
2. Hierarchy window > right click
3. 3D object > terrain
4. Go to terrain settings > import raw
5. Select a raw file
6. Shrink "Import Heightmap" window horizontally or vertically

Actual Result:
Import heightmap keeps shrinking to the minimum size, making UI elements unusable

Expected Result:
Import heightmap window should restrict the user to shrink it beyond a certain limit, where the UI clearly laid out

Note:
"Export Heightmap" window doesn't allow the user to shrink the window beyond the certain limit which is correct behavior

Environment:
Windows and Mac

Occurring with:
2018.3.0a4, 2018.3.0a3, 2018.2.0b10, 2018.1.6f1, 2017.4.4f1, 2017.1,4f1