The brush is always rendering and generating heightmaps, textures, and details in square shape

Steps to Repro:
1. Create a new or open attached project
2. Hierarchy > Right click
3. 3D Object > Terrain
4. Select paint texture tab and hover over terrain

Actual result:
1. The brush is being rendered as square
2. An error occurs on selecting paint texture tab
3. Heightmaps, textures, and details are being painted in the square shape

Expected Result:
1. Brush rendering changes according to brush selected

Environment:
Windows and Mac

Occurring with:
2019.1.0a10

Working with:
2019.1.0a9, 2018.3.0b11

Stack Trace:
Texture2D: Unsupported texture format for ReadPixels (R16 UNorm, 9). Use SystemInfo.IsFormatSupported(format, FormatUsage.ReadPixels) to check supported formatsUnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)