What I expected to happen was...:
Create a copy of a filled map using the cartography table.
What actually happened was...:
I was able to create 3 copies of the filled in map, and keep the empty map I would have used.
Steps to Reproduce:
1. Right click on an empty map to fill it in.
2. Access a cartography table.
3. Place the filled in map in the top slot of the table.
4. Place an empty map on the bottom slot of the table.
5. Hover your cursor above the output slot of the table, which should show 2 copies of the map.
6. Press the hotkey of one of your hotbar slots. (ex. Press "1" for the first slot)
7. The 2 copies of the map will be duplicated: 2 of them will be placed in your hotbar, while the original filled map and empty map will remain in their slots.
8. By emptying the hotbar slot and repeating Step 6, you can create infinite copies of the map without using any resources.
Video showcasing bug: https://youtu.be/bfNDuFPDOZw (File size was too large to attach.)