In the Video it appears that only the Circular Face of the end Body and the Cylindrical Faces of the other chosen Bodies have been selected?
The whole Body must be selected to enable it to be Copied.
Hit the Items Icon and from the pop out Select the Bodies you want to Copy
A partial Selection is indicated by a Blue Line on the left, while a whole Body Selection shows full Blue:
Hi, as Gelphyn mentioned you will need to select the entire body to make the duplicate copy.
If you will like to have only that part, after you have made a duplicate copy:
Tap to select unwanted parts
Tap on delete to remove them from the duplicate copy while still having the original body as backup against unwanted results.