Steps to repro:

1. Open attached project and 't1' scene;
2. Notice that there is terrain with Default Standard terrain shader;

Expected result:
Terrain material is rendered smoothly.

Actual result:
Terrain material is overspecular (see attached actual.png screenshot).

Notes:
- Reproducible in 2017.1.0a5, 5.6.0f3, 5.5.2p1;
- Reproducible on OSX 10.12.3 and Windows 10;
- Reproducible only with Nature/Terrain/Standard shader; not reproducible with Standard, Nature/Terrain/Specular and Nature/Terrain/Diffuse shaders;
- Reproducible in Editor and Standalone Player.