OK, so I'm a total newb to Carrera with v7 but I'm familliar with a number of other aps and don't have this problem with any of them, not even Bryce.  When I start a scene that has a terrain object and add a second terrain object, Carrera only renders one terrain.  What the heck is it doing.  Yes, the second terrain was inserted so it is in the same scene.  Have the same problem with a water object.  It's there in preview, I expand it so that it should be visible but it doesn't render.
     It doesn't seem to have the same problem when it comes to DAZ/ Poser content.   No problems at all loading, dressing and posing figures and the render engine does a really nice job on figures.