Steps to reproduce:
1. Open the attached project (Test Project)
2. Open the Assets/SceneTest.unity scene
3. Switch to Game Window
4. Observe, the blacks texels all over the objects
5. Select "couch_colifornia" in Hierarchy View and set Scale X to 1
6. Open Lighting setting
7. Bake the scene with static baking (Progressive Lightmapper)
8. Switch to Game Window
9. Observe, the blacks texels are gone

Expected result: Rendering without black texels
Actual result: The blacks texels all over the objects

Note:
Feature introduced in 5.6.0b6

Reproduced with: 5.6.0b6, 5.6.0b7