Original issue: EnigmaticaModpacks/Enigmatica6#1196

Forge 36.0.42
Inventory Essentials 2.3.0

When playing on a server, it is possible to duplicate an item by first throwing the stack from your inventory using ctrl + q, and then clicking the now empty slot while still holding ctrl. A new item of the same type will then appear in your inventory.
(This exploit does not work in creative mode)