Locking maps can duplicate them

The bug

Locking maps using the cartography table duplicates them if there is more than one map in the input slot.

How to reproduce

1. Create a map
2. Clone it
3. Place the two maps and a glass pane in the cartography table
4. Take the locked map (left click) and place it in your inventory
5. Pick up the locked map again
   → You hold 2 instead of 1 locked map