Minecraft wiki entry for Development_versions, associated text: MC-13723 – The horses do not make any sound but do open their mouths.
MC-13731 – Horse can climb ladders/vines.
MC-13788 – Horses graze on non-grass blocks, also underwater.
MC-14114 – Leashes break when riding a horse.
MC-14604 – Cannot tie wild horses and foals.
MC-14930 – Horse armor not keeping enchantments when dropping from a horse.
MC-15423 – Crash due to corrupt pack.png in texture pack.
MC-16051 – horses break lead when being lead when they stop to eat grass.
MC-16156 – Unable to move previously ridden horses after reloading the world.
MC-16168 – Opening inventory on wild horse allows you to saddle it up.
MC-16182 – Problem with horse movement.
MC-16196 – Horses not running fast in creative.
MC-16229 – Horse – shift key locking.
MC-16381 – Tamed donkey/mule drops 2 saddles on death.
MC-16415 – IllegalStateException: Server tried to update attributes of a non-living.
MC-16421 – Horse speed does not remain constant.