I'm just learning Motion but this I know about nests-- don't cut into them!
Each time you slice into a nest (sounds like you've done two slices to extract the "middle"
you duplicate the contents and use up more memory. And copying just this sliced section merely copies all contents from the second of three identical containers. I call it the SAS-- Sorcerer's Apprentice Syndrome. Avoid it by doing what John suggests-- step into your nest, highlight and copy the clips you need.
- Loren