Mobs that are in water jump really high. I believe this is due to chunk borders, as I only notice it when come back to an area. Additionally, if I stay in the area for a while, nothing happens.

I have a cow pen with water on one side. That side always has cows outside of the pen whenever I return to the area. On rare occasion I actually catch the cow flying across the screen, it visually looks like a glitch. 

I was able to catch a wandering villager alpaca do the glitch, the video is too large, but an image is attached. I believe the cows fly horizontally because of entity cramming, while this alpaca flew because of the water.