zombie villager 'jughead' glowing outline error

So, i was continuing my experiments with spectral arrows when i shot a zombie villager and i realized his head area looked strange. when i took a closer look it looked like the spectral arrow was outlining an invisible normal zombie head as well as the actual zombie villager head.

~~~_{HOW TO REPLICATE}~~~
1. spawn in a zombie villager.
2. shoot him with a spectral arrow.