I Created A world in 18w43a and i have updated it to every new snapshot when it came out.
when i updated it to 18w47a today a structure i had built was duplicating itself at -16 97 -8 i destroyed and stayed afk on the world for about 10 mins. when i came back the duplicating structure was back again. (The original Structure is a bamboo farm and is located at -6 79 144)
Duplicates MC-139693 (fixed).