What I expected to happen was...:
Riding a horse, in single player, towards various one block high edges and natural terrain, expecting it to automatically climb.
What actually happened was...:
Roughly 90% of the time, my horse will get stuck and jitter in place on one block high edges. Stubbornly continuing to walk forward will eventually damage the horse. If not damaged, dismounting will apply the expected amount of damage to the horse it would have taken.
Steps to Reproduce:
1. Mount a horse
2. Walk towards a one block high step, causing the horse to get stuck and jitter. Horse may take damage.
3. Repeat step 2 multiple times
4. Dismount, horse may take damage
Looks like this is probably a duplicate of MC-100830. The issue is very similar and the same message gets spammed in the console, however, the issue is MUCH worse than it was in previous versions. Also, the player can take (massive amounts of fall) damage from this, killing the player instantly.
Edit: the issue is probably best demonstrated trying to ride a horse up a staircase. MC-100830 doesn't mention it occuring with full blocks or slabs, but from my experience this has always been an issue with full blocks as well in prior versions, but has been less common to occur on full blocks, and most common on stairs.