Dan - how would flattening the terrain make any difference? The reason I'm duplicating it is to retain the dimensions and location; I'm just changing the heightmap. Ray - I checked Brycetech, but no luck. I didn't find any downloads there at all, just tutorials, galleries and links. :-( I checked, and both terrains have a parent of none. And yeah, I've been creating one, sticking it in the user library, then creating the other. That way I can bring them both into a single scene. It's a pain though, and I wish I could figure out what's going on. Example of what I'm doing - I've got a heightmap of a window with fiddly stuff inside and an arched top. To make a piece of glass to fill the empty spots, I'm duplicating the original and using an almost-identical heightmap which has a solidly filled arch. (Can't use a default primitive without booleaning it to the right shape, sadly.) I want these two terrains in the same place and with about the same dimensions. However, when I duplicate the first 'frame' terrain and rename it 'glass', then enter the editor and load a new heightmap, both the 'frame' and 'glass' terrains change to the new one. The only terrain I want to change is 'glass'. Make sense? Thanks, - taerin