The armor stand could in 1.12.0 wear certain items as they were armor aka raw chicken/salmon/rabbit,Pufferfish and slime and now in 1.13.0 it doesn't wear it but instead moves it to the item holding slot which seems to remove the item placed there prior to the 1.13.0 update.
It’s never mentioned in the changes of 1.13.0 so I don’t think it’s intended to be like this.