Put the summary of the bug you're having here

What I expected to happen was...:
My Minecraft world would load up as usual. 

What actually happened was...:
Pre-existing chunks in my world are duplicated to random places near its original location. For instance, the chunk containing my carrot farm was duplicated and placed 30+ blocks away. I discovered this as the carrot farm, which was placed on grass, suddenly had an exact copy loaded nearby in a sandy environment. 

Steps to Reproduce:
1. Load up an existing Minecraft world.

2. Check for any chunk-sized areas of blocks that appear out of place? (Very vague but I don't know any other ways to check. Maybe create something close to the ground that can be easily recognized if replicated in a different area).  

3. If none appear, reload again to check for changes.

4. Repeat checking. 

In the picture below, the duplicated carrot farm can be seen in the foreground. Close to the upper right corner of the screen, the same and original carrot farm is located. Please believe me when I say that I did not forge this or simply recreate the farm myself; I do not know why the game is duplicating pre-existing chunks.