Taming horses is impossible

Normally, when trying to tame horses, the player mounts them and gets thrown off a couple of times before heart particles appear after a few attempts and the horse is tamed. When I created a world in 15w43a I tried to tame several horses, but I would remain sitting on the untamed horse for several minutes. Dismounting and mounting again had no results. (I apologize if I am making a silly mistake here)