What actually happened was...:
Bug seems to only be a bug in multiplayer, but what happens, you right click a horse, get on, and crash. And when you try to join again, you get kicked instantly.
Steps to Reproduce:
1. just right click any horse in creative/survival
Duplicate of MC-13628, please use the search function to see if your bug has already been submitted. Currently over 54% of tickets are being closed as duplicate.