Mobs see void as a solid block

While experimenting in my snapshot world, I decided to have a little fun with a game of tag: Zombies and Villagers. However there were holes in the ground and I found this behavior odd: they would walk straight toward their target without regard of the obstacles. I have a video here:

https://www.youtube.com/watch?v=m2EsNRNCXZo

Offscreen however I found that the same behavior applies to all walking hostile mobs targeting players. They seem to try and navigate around fire though. This appears to be intended.