Steps to reproduce bug:
1. Open "Terrain Detail And Tree Bugs" project
2. Open "Terrain Mesh Detail" scene
3. Focus "Cube" object
4. Open "Terrain Mesh Detail Bug" inspector
5. Select one of the grass in Paint Details
6. Try to draw with brush on the terrain
7. Observe strange square patterns

The strange pattern on the grass is the result of the number of vertices in a single grass patch exceeding the hard limit of 65 thousands. We added a console warning message in 5.2 version of unity when this happens.

Tree Distance, Billboard Start, Fade Length and Max Mesh Trees have no effect on "SpeedTree" type of trees. We just added an info box on Terrain Inspector to better communicate this information to the users in newer versions.