Steps to reproduce:

1. Download the attached project and open AdditiveLighting_00_Master scene (Assets > Multi-Scene Tutorial > Scenes)
2. In the same folder (Assets > Multi-Scene Tutorial > Scenes), the rest of the scenes, right-click on them and select Open Scene Additive
3. In the Hierarchy view, select all the additively loaded scenes (except for AdditiveLighting_00_Master and AddtiveLighting_05_Occluders), right-click on them and select Unload Scene
4. Bake the lighting
5. Notice that the spotlight appears stretched and other lightmapping artifacts might be visible

Notes:

- Only occurs when Static Batching is enabled
- Only occurs in multi-scene setups
- Only occurs in auto mode
- Lightmap index gets set to -1 in auto mode