Since 20w12a, on a server, if you get a mobhead after server is 20w12a, when you place it, it always uses the Steve skin. For example, suppose you get zombie villager leatherworker head, on the ground and in your inventory as an item it has the right skin, but once you place it on a wall or something, it changes to a Steve skin, but if you break it and pick it up again, will show as the proper skin. Also, heads that were obtained before updating to 20w12a work fine and show the proper skin, even if broken/picked up/ place again. This only affects heads obtained in 20w12a.