So I was riding my horse, and I clicked the meat grinder (my character then unmounted and got on the grinder). After I made some sausages, I left click on the horse since the horse was in the same place (or you cand left click anywhere), and I ended mounted up back on the horse ... but on the wrong side - went straight under it. Now I am riding the horse from underneath - see the gif http://i.imgur.com/tPZBS61.gifv. It's only a visual bug, since you can dismount, and if you switch instance (ex. enter a mine), it turns back to riding normally.
It's quite funny but I'm not into bestiality ...