I had my realms world downloaded locally to edit a few setting on my windows 10 edition and noticed the world became available for me to join as a friends lan game on my console, noting that this is from the same account logged into two different devices at the same time, so out of curiosity I attempted to join from my console and to my amazement it successfully connected and spawned me into the world exactly where I had respawned from the last save, and with my entire inventory + ender chest contents duplicated. The clone player had a (2) added to it's name, my name, and seemed to be a unique player once in the world because I couldn't see into the clones ender chest from my primary avatar  or vise versa, except for the glaring fact that the clone had all my gear. So I feel safe in assuming this is not intended behavior. I dug through other reports of player duping but couldn't find this exact scenario or anything even close so figured I'd report it and if it was actually a duplicate report then my apologies, and at least the matter is known and hopefully being addressed in the next update release, if not then great, now you know.

To Recreate:

• Log into Minecraft Bedrock On Windows 10
• Log into Minecraft on Xbox One Using Same Account as Windows 10
• Open A Survival World on Windows
• Now That world is available as Friends Lan Multiplayer 
• Join on Xbox and Watch as Player, Inventory, and Ender Chest Gets Duplicated