When you place an item in an item frame with a comparator behind, you can duplicate the item when you leave/join the world if the item frame and the comparator are not in the same chunk.

This video shows how it works:
https://www.youtube.com/watch?v=mXBDcQP-U7E&list=UU_zlzZpJOmvr1WpS3wh7xyg

Dupe of MC-51610