Usually, horses can walk up 1-block-tall inclines automatically, without the need to jump. It seems in a recent update, carpets now raise the y-value of the player slightly. This has caused horses to no longer be able to walk up blocks with carpets on top of them.
Steps to Reproduce:
Create a platform with a one block incline.
Place carpets on top of the incline.
Try to ride a horse up the incline.
I don't think screenshots are necessary, but I will provide some if asked.
Horse rides up blocks with one-layer snow, but not with two layer snow and carpet.