When killing the spider part of a spider jockey, the skeleton glitches out and becomes invisible and may look like it is somewhere else

I was wandering a desert, killing mobs, when I came across a spider jockey. I killed the spider, and the skeleton disappeared. I started hitting around where I thought it was, and I saw a skeleton die maybe 20 blocks away. I heard the death sound as if it was right next to me, however. The invisible skeleton bug can also be seen in Etho's Uncharted Territory Episode 12 at about 7:15.