At my home desktop, when I reject photos with an x, I then use the "Create new folder within the (Name) folder" option by right-clicking. The rejected files are moved to that new folder labeled, "Rejects." So if I originally have a folder of 60 images and reject 10, then I will have 50 good images in the parent and ten in the "Reject" folder. Perfect. Version 8.3.1
I'm teaching a class now and when demonstrating this technique, the rejected files are copied, (not moved) to the "Rejects" folder and also stay inside the parent folder. So I now see the 60 original files in the parent folder plus a child folder with the ten rejects. When I check my Finder, there are in fact duplicate files inside the "Rejects" folder.
It's happening on my teacher station and the student work stations.