World returned to and old file MEANWHILE I WAS IN GAME

Ok so, I was in my survival finishing my Enderman Farm. When i ended it, i farmed a bit, got my things repaired with mending and took some enderpearls; I crossed my bridge puting slabs in both sides, left and right; I arrived to the End Island and I picked my yellow shulker box too. Then I went to cross the portal again, but before of that I realised that I was lagging: when building the farm I set my render distance to 32 just for fun, so I put it again to 10. After that, I turned back since I forgot one pickaxe in a chest in the farm, and the bug happened:

Without exiting the game or the wolrd: JUST TURNING ARROUND AND LOWERING THE CHUNKS, i found this:

http://i.imgur.com/aE6dY22.png

The shulker box and behind it there was my farm as it was like hour and a half before. Quite all my progress was lost: the endermite, the water source bloks avobe the farm, etc etc etc.

http://i.imgur.com/FkijB8n.png

As you can see, I still had my enderpearls and my repaired weapons...

I logged out and when logged in again I found myself here, building it:

http://i.imgur.com/b0Mt3BP.png.

What has just happened? 😞