How to reproduce:
1. Open the attached project
2. Open the main.unity scene
3. Note how both cubes are rendered differently, although they should be identical
4. Play the scene and notice how it is rendered when one cube changes position
5. Set one of the directional light's (from hierarchy LightFill or LightKey) render mode to Not Important
6. Note that if the light is set to "not important" the object renders properly even though the light still has an influence on the lighting of the object.

Not reproducible: 5.4.0b15