Steps:
1. create a new scene
2. save the scene
​3. Create another empty scene and save
4. To the main camera, add a new component script and give some name - double click it on the component to open monodevelop
5. Now save the script in mono and come back and do another file save
6. Toggle between scene 2 created in step 3 and go back to scene 1

Click on main camera and note that the script component is not persisted any more the asset remains, so we can drag and drop again to the main camera

Screencast:http://screencast.com/t/JsM3YiXl3DU2