Why are the terrains in my seperate scenes linked when edited?

When I make a terrain and 'save scene as' Untitled1. Then While in Untitled1. I 'save scene as' Untitled2..

1. Now I have (scene) Untitled1.
2. and (scene) Untitled2.
3. When I edit the Terrain in Untitled2 why does it edit also the terrain in Untitled1?

Is this suppose to happen?

Also when I

1. make a prefab of a Terrain,
2. duplicate it,
3. change the name.
4. Make a prefab(of the newly named)
   
5. It still edits both terrains when I edit one....

Why are the terrains in my seperate scenes linked when edited?