Record Button

Once you have your scene composed or re-edited to your like, you must click 'Record' button to register your composition or changes to the Timeline. If you leave SC mode without record your work, it will be gone next time you come back. When a composed scene is being recorded you will see a letter 'E' flashing momentarily and stays on top of the corresponding frame in the Timeline Strip. This is to indicate that the scene has been modified in the current timeline session.