While playing, and having horses, if i go anywhere far away, even within the map area, my horse and donkey will disappear, as if they never existed. it will most likely effect mules too. though there is a workaround until fixed by Mojang. Just save and quit the game, then launch the game world the horses in question are located, and they should return. But this may or may not cause the host of a LAN only game to shut down the game for all players until he/she returns. either way...it should be fixed for the sake of...small convenience. it's not game breaking thank goodness...but quite annoying.