What I expected to happen was...:

The hand will render no item when entering a new world

What actually happened was...:
The item I held in hand before creating a new world rendered although I didn't have it

Steps to Reproduce:
1. Enter a world, grab any item (I used an eye of ender)
2. put in your main hand
3. leave world

4. create new world

5. tab out of minecraft while world is creating

6. wait until world is generated

7. go into minecraft again

The item will be visible in your hnd while in pause menu (and for a short moment after leaving it)