I sat on a horse (with saddle and gold armor, if that would make any difference), logged out and in again and the horse was gone. (Will return now to see if it's back in the area where I first mounted it.)
No pic necessary, it would just show me, alone, in a desert.
Duplicate of MC-47508 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.