Related to: https://fogbugz.unity3d.com/f/cases/resolve/776013/

Repro Steps:
1. Open a new project with Unity 2019.2.0a4
2. Create a Terrain
3. Create a new Cube gameobject in the Scene
4. Create a prefab out of the Cube by dragging it from the Hierarchy to your Assets folder in the Project window
5. Select the Terrain
6. Go to the grass and details tab
7. Edit Details -> Add Detail Mesh
8. Add the Cube prefab as a Detail mesh to the Terrain
9. Edit Details -> Add Grass Texture and add one of the built-in textures
10. Paint the Cube on to the Terrain
11. Delete the grass texture from the Terrain

Result: You should see the rendered cubes change in appearance after removing the grass texture from the Terrain