Whenever someone gets an item via the give-command the PlayerDropItemEvent gets called and if cancelled the player gets one more of the item then specified. Not twice, just one more.

Using Spigot 1.15.2. The event only gets called once. As written in the javadoc the event should only be fired if a player drops an item, but not when getting one. The event does not get called when the player picks up an item lying on the ground.

Video showing the bug: https://youtu.be/8cl-em3S7Kg