Oh, you mentioned symmetry above. Carrara is much better now (version 5 pro) but it still manages some sort of quantum entanglement of duplicates in the vertex modeling room. I have had the habit from several version numbers back of selecting the duplicate and hitting "detach polygons" a couple of times. And jumping into the Assemble Room as well, where inverted normals (another common problem Carrara has with duplicates) are easier to see, in case I also have to hit "reverse surface normals."