Horses disappear when dismounting

The horse disappeared on pressing left shift to dismount. This has happened a few times with different horses, all tamed and saddled and a few named, and one skeleton horse. The saddle and any armor also disappear.

Steps to Reproduce:
1. Tame a horse and ride it around a while
2. Dismount with left shift
3. Sometimes it happens and I can't find the horse anywhere, sometimes it doesn't.