I stored my items in a chest, accidently logged in with another open minecraft window(I would to check how I build my redstone in a creative single player world but logged in to the server). My items duplicated.

What I expected to happen was:
The items aren't in my inventory, but in the chest where I stored them.

What actually happened was:
The items were in my inventory AND in the chest where I stored them.

Steps to Reproduce:
1. Log in to a server(Let's name this window MC1)
2. Open another window with minecraft (Let's name this window MC2)
3. Make MC1 active
4. Run to a chest
5. Store the items
6. Quickly login to the same server with MC2
7. MC1 got kicked for "Logged in from another location"
8. In MC2 the items are in your inventory and in the chest, they are both useful and aren't ghost items are something.

PS: Merry Christmas! (a bit to late but...)
And tell JIRA that they need to be better, it's always down.
I needed to rewrite this report many times because when it was done, JIRA got down.