When updating mobs that are wearing armor in version 1.8.9 and before, directly to 18w19a and after, all mobs swap armor slots with hand slots, resulting in the mobs wearing items, and holding armor. This can also cause skeletons, wither skeletons, and zombie pigmen/piglins to be empty handed.
Steps to reproduce:
Spawn a mob with armor (only boots and leggings work) in any version before 15w31a
Update the world directly to any version after 18w16a
All mobs that were previously wearing armor should now be dual wielding leggings and boots
Here is a list of all affected mobs:
Zombie
Baby Zombie
Zombie Villager
Baby Zombie Villager
Zombie Pigman
Skeleton
Wither Skeleton
Armor Stands
Villager (Not Visually Noticeable)
Linked issues
is duplicated by 2
Attachments
Comments 3
Affects upgrading worlds from pre-1.9 to 1.20.5
[media]
Duplicated by MC-264319, which has a Mojang priority, whereas this ticket does not but is now fixed in a future version. It could likely be marked as a duplicate at least the snapshot is released.
gegy
Can confirm in 1.18.1.
Note that armor stands are also affected.