bug with horse going up through stairs

while going up a ramp of cobble stone stairs with my horse(in leather horse armor)  after some seconds the horse starts going slow and looks buggy going forwards and backwards like half a block or 1/4 of a block 

What I expected to happen was...:
I expected the horse to keep going at the same speed it started at and not looking buggy

What actually happened was...:
the horse looked buggy and slowed down

Steps to Reproduce:
1. make a ramp of cobble stone stairs 3 stairs wide and as long to ride the horse for more than 5 seconds
2.get a horse thats already tamed and with a saddle( ready to be ridden)
3. go up the cobble stone stairs