Horses can run up a one-block-step incline smoothly, but not when the incline is made up of stairs or slabs.
Steps To Reproduce
Create a staircase using slabs or stairs
Run up the incline whilst riding a horse
Notice the horse slowly jumps up each 1/2 block step, instead of running up smoothly.
See attached screenshot for an example setup to test.
Reported for test and fix.