Item duplicates after placing it in crafting table/anvil/etc...

Step-by-step instruction:

1. Load and play the world;
2. Open any item interface (f.e. Crafting table);
3. Push all items what you need to slots;
4. Leave interface using Esc key (or "B" in Xbox gamepad);
5. Leave the world;
6. Load the world.

Items overload doing unplayable worlds.

 

Video on YouTube