You probably didn't Keyframe correctly.

You're going to be using keyframes with your stick figure or whatever animation, and your scenery, like you said, is on a different layer under it. If you press F6 (insert keyframe) or F7, everything will be fine. Keyframes mark a new frame position. Normal Frames don't. So if you do your animation in keyframes, and want to change views or a scene or something, unlocking the scenery layer , clicking the frame, and deleting it will result in the entire thing being deleted. A frame is used for still images or double frames, Key frames mark a change, or just pressing F6 or F7 to do so. When you go to add a new background for a new scene, unlock your scenery layer, click on the current frame you're on with your animation, and press F6, then F7. And you will be fine.
Either that or upgrade your software?