Record
Button

Once you have your scene composed or modified to your like, you MUST
click 'Record' button to register your composition to the
Timeline. If you leave current scene without record your composition, it will be
lost forever. When a composition is being recorded
you'd see a letter 'E' flashing momentarily then staying constant on top of
the corresponding frame in the Timeline. This is to indicate
that the scene has been modified and the change has been saved. The letter 'E' will stay with respective scene until the end of current TE session.