Buggy AI for skeletons riding horses

If you spawn in a skeleton that is riding a horse, then go into survival mode and encourage it to attack you; if it can't find an obvious path to your location then it will start spinning on the spot and won't stop until it stops targeting you. This also seems to occur when the skeleton moves into the same spot as you, although it can still attack you.

/summon EntityHorse ~ ~ ~ {Tame:1b,Passengers:[{id:Skeleton,HandItems:[{id:diamond_sword},{id:diamond_sword}]}]}