Once the player is mounted the horse will run about randomly and will occasionally get stuck in corners. When this happens, use a wyvern or other large tame to box the critter in! This will keep the animal confined and keep it from running in to spike walls or aggressive wild dinos!
Quick tip: I was trying to tame one at my house and it bucked me off and my other tames thought it was hurting me so they killed it. Long story short, put all your other tames on passive if you want to tame it at your house.