Steps to reproduce:
1. Create new project
2. Add any object and material
3. Change material shader to "Mobile/Bumped Specular"
4. Set object to "Lightmap static"
5. Bake lights and observe object become darker
6. If you set the directional light to "Baked" only, the object becomes entirely black

Expected: Should look mostly the same as Bumped Diffuse, just with more highlighted reflections
Actual: Object turns out either darker or black entirely

Reproduced on: 2017.3.0a3, 2017.3.0b10, 2017.3.0b11, 2017.3.0f1, 2017.3.0f3, 2018.1.0b2
No repro: 2017.1.3f1, 2017.2.1p2, 2017.3.0a1, 2017.3.0a2