Unsaddled and/or untamed horses cannot climb a single block.

Put the summary of the bug you're having here

What I expected to happen was...:
Untamed and unsaddled horses are confined to a single plane or lower. They cannot move 1 block higher unless saddled and ridden.

What actually happened was...:
Horses used to be able to freely move about in the same manner as villagers. They could climb a single block up. Now that feature has been disabled. They congregate in low areas like leaves around a drain, and do not move upward, not even if pushed. The only ways of moving them is to ride them out of a low area or put stairs in front of them. Young horses can move up a block but not grown horses. I find this depressing.

Steps to Reproduce:
1. Find some horses that are in an area where they could climb a block.
2. .Watch them..
3. Watch them some more.
4. You get the idea. They do nothing. Occasionally one might drop to a lower block, but it will never go back to the original higher level. So much for wild horses roaming free. Maybe they are all geriatric.