Minecraft 14w11b, Minecraft 14w18b, Minecraft 14w19a, Minecraft 14w20b, Minecraft 14w21b, Minecraft 14w25a, Minecraft 14w26b, Minecraft 14w26c, Minecraft 14w27b, Minecraft 14w28a, Minecraft 14w28b, Minecraft 14w29b, Minecraft 14w30a, Minecraft 14w30b, Minecraft 14w31a, Minecraft 14w32a, Minecraft 14w32c, Minecraft 14w32d, Minecraft 14w33a, Minecraft 14w33b, Minecraft 14w33c
Windows x64, encountered on other platforms also.
Attached screenshot and minimal world repro. If you stand at the location indicated in the screenshot and save/reload the world, you will hit the bug.
Root cause has been narrowed down to:
Item frame with some contained item at X=0 / Z=0 in chunk
Mounted on block in adjacent chunk
Behind that block, a comparator is sensing the item frame
Stand in a chunk adjacent to the chunk containing the item frame, save and load the world, and all entities in the chunk with the item frame will be duplicated a huge number of times.
This is an item duplication glitch that involves the new comparator measuring item frame feature in snapshot 14w18.
How to Replicate This Bug:
1.) Find the east/west edge of a chunk. (Preferably using F3)
2.) Place any redstone current-carrying block on the west side of the chunk edge.
3.) Place an item frame on the block, facing east.
4.) Place a comparator next the block, pointing the opposite direction that the item frame is facing, so that the comparator is in a different chunk than the item frame.
5.) Put any block you want to duplicate into the item frame.
6.) Quit and re-join the world. You will now have a stack of item frames and the item you put in the frame.