Mod note: Description from Hafydd
When using Minecraft 1.13 to open a world created in Minecraft 1.12.2, regardless of whether "optimize world" / forceUpgrade is used, in all north- and east-facing double chests the items from the top half are swapped with the items from the bottom half. In south- and west-facing double chests, this does not occur.
To reproduce this bug:
- Create a new superflat creative-mode world in Minecraft 1.12.2.
- Put down 4 double-chests, each facing in a different direction (pictured in 1st attached screenshot).
- In each of the 4 chests, put a diagonal line of items spanning the width and height of the item grid (pictured in 2nd screenshot).
- Save and close the world (a ZIP archive of the 1.12.2 save file at this point is attached).
- Open the same world in Minecraft 1.13.
- Observe that the north- and east- facing chests have been rearranged (as pictured in 3rd attached screenshot).
Note: I'm aware this is a duplicate of an existing issue and the current status is "Won't Fix", but it was requested by a developer that a more detailed issue be created so this problem can be looked at in more detail:
After updating world from 17w46a to 17w48a, items that used to be in the top three rows of north- and east-facing double chests are now in the bottom three rows, and items that used to be in the bottom three rows are now in the top. (south- and west-facing chests are unchanged.)