How to copy a part of a sequence diagram in EA?
Copying and Pasting the contents of a sequence diagram only copies the objects, fragments and comments but not the messages. Also all the entities copied are placed on the top of diagram. There is a better way - Copy Diagram and Paste Diagram.
The objects copied are not links but new instances. If you want links to existing instances to reduce the number of instances in the diagram, add the links to the existing instances and update the messages between the existing instances. Select the messages to delete, unselect the links to the existing instances to keep, and then delete the rest.