does LoadLevelAdditive() call MonoBehaviour.OnLevelWasLoaded ?

Loadlevel does, but LoadLevelAdditive appears to not call MonoBehaviour.OnLevelWasLoaded?

unity bug?

You can track the progress using LoadLevelAdditiveAsync using the class AsyncOperation

Additive does not have that callback hooked to it, as a level isnt technically being loaded. Objects are just being added to the current scene.