Horse Bug - Cannot Climb Stairs & Slabs Smoothly

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.