Occasionally while riding a tamed horse when I save/quit; the next time I load that save game file my character is on foot and the tamed horse I was riding has disappeared from the world. This has occurred in 1.7.5, 14w11b and 14w18b and on several versions of Java 7. This has never occurred with Donkeys or Mules (granted that I don't use them too often).

The Tamed Horses wear Saddles, Armor, and 1 of the 3 that despawned had a Name Tag put on it. Typically this occurs when I go to save after travelling long distances into newly-loading chunks I've never been into. I suspect it could be a bug that occurs when you go to save/quit while riding a tamed horse when your Allocated Memory is at or near 100%.