Not Saving

Whenever I save and exit my single player world, the game deletes the horses I have tamed and whatever changes to the environment (placing/breaking blocks) are undone.

What I expected to happen was...:
Saving and exiting my world to quit the game.

What actually happened was...:
Tamed horses/donkeys are deleted and blocks placed/removed are undone.

Steps to Reproduce:
1. Play a Single Player world
2. Tame a horse or place/remove blocks.
3. Save and Quit to title, then reload.