The information in this article applies to:
When I select a terrain object, like a hill, and press the Delete key on my keyboard one time, the hill is not deleted. I seems instead to remain on the drawing, regardless of what I do. How do I get rid of it?
Once deleted, terrain objects will appear to remain in the drawing. In fact, they have been deleted, but the terrain must be rebuilt before this change will be reflected in the drawing.
Alternately, if you have a 3D Camera view open when objects are deleted from the floor plan, the terrain will rebuild automatically.