When feeding a baby horse,giving him one piece of the food his skin will update to a fully grown horse, while his properties (hit box/ tame ability) are staying not ''bugged out'', he just isn't full grown yet. Like before you need to feed hem around 32 pieces of food to make him fully grown but his skin is updated after one piece. relogging will undo this visual bug and shows the right stage of growt of the said horse.