To reproduce:
1. Open "new unity project 5"
2. Open scene "test"
3. Notice how in scene view the grass circles are different (one with some sort of border and one without. These are the same textures, just different brush slots)

Note: this seems to occur since the 5th terrain texture when using Nature/Terrain/Bumped Specular shader. The issue does not reproduce when using vertex lit rendering path.