When loading a crossbow that is part of an oversized stack, all items in the stack will be become loaded with the projectile. The stack can then be split and each crossbow will still have a projectile loaded, but the projectiles can be fired separately. As a result, multiple projectile loaded from the same single item can be fired, representing a duplication glitch particularly with projectiles that can be picked up. The reverse also works: merging loaded crossbows into a single stack to condense multiple projectiles into one.

Steps to reproduce

1. Obtain an oversized crossbow stack: /give @s crossbow[max_stack_size=3] 3
2. Load the crossbow stack using 1 arrow.
3. Split the crossbow stack into individual items.
4. Fire each crossbow into the ground.
5. Pick up 3 arrows despite starting with only 1 arrow.