Ability to duplicate items via dropper and crafting table

I made this private since this could be considered an exploit.

 

My siblings discovered an item duplication glitch for items in the crafting table. Using the contraption in the attached screenshots, they can load up items such as diamonds, gold ingots, or lapis lazuli into the dropper or dispenser. The redstone burnout clock will continuously spit out items into the player's inventory.

 

While the items are being loaded into the inventory, the player clicks into the crafting table and starts spam clicking the block form of the item on the left side. This will craft the item, but the spamming allows the items to be duplicated.

 

We were playing on our Realms world, so there are a few possibilities for the root cause:

1. Client-server desync could be causing the player to end up with more items than they actually have as the Realms server tries to sync with the rapid inventory updates (currently untested, will update once I have one of them test it).
2. If there is a faulty item count check, there could be a problem with desync between when the code checks for item count and when the code creates and loads the item.
3. Something else.