The bug

The model for the piglin helmet is incorrect in 1.16-pre3, the helmets are smaller as if the player helmet model is used instead.

To reproduce

1. Run the following command

    /summon minecraft:piglin ~ ~ ~ {NoAI:1,ArmorItems:[{},{},{},{id:diamond_helmet,Count:1b}]} 

   → Notice that it looks smaller compared to the previous pre-release. It is not wide enough to fit in the piglin's rectangular head.

2. Enable programmer art
   → The helmet worn by the piglin is affected by the programmer art resource pack, thus revealing that the piglin helmet model is not being used anymore and it reveals that the player helmet model is being used instead.