Grass block not updating when a sheep eats from it

Exactly as the title says. A sheep will eat the grass from a grass block, and it's wool will reappear. However, the block will not change from a grass block to a dirt block when the sheep eats from it. I was trying to make something with an observer, where the observer would be updated from the grass block changing. That's when I noticed that the block wasn't changing at all.