Steps to reproduce:
1. Create a new project
2. Create a new scene
3. Set the Directional Light to baked
4. Set it to cast soft/hard shadows
5. Create a cube, mark it as static, set the position of it to X:0 Y:2048 Z:0
6. Bake the lightmap

Expected result: Artifacts should not appear
Actual result: Artifacts appear on the top face of the cube

Reproduced in: 2017.1.0b1, 5.6.0f3, 5.5.3f1, 5.4.4p4, 5.3.7p3