Riding an entity with slow falling will not stop fall damage

The Bug

When riding a horse with slow falling, both you and the horse will still take damage upon landing, even if both of you have the slow falling potion effect. Note that the horse still falls slowly regardless of if the player is riding it or not, it just doesn't prevent the damage.

Steps to Reproduce

• Summon a horse and give it the slow falling effect.

  /summon minecraft:horse ~ ~ ~ {Tame:1b,SaddleItem:{id:"minecraft:saddle",Count:1b}}
  /effect give @e[type=minecraft:horse,limit=1,sort=nearest] minecraft:slow_falling 999 0
  

• Relog, to avoid MC-121788
• Switch into survival mode, mount the horse, and ride it off a high cliff.
• Wait for the horse to slowly fall to the ground. It still takes damage.