Skeleton on a skeleton horse

How many I play minecraft, this is not seen. Created the world. And on the 4th game day, I heard lightning, and 4th skeletons appeared on the skeleton-horses. This is most likely some kind of mistake.

Otherwise it is a terrible imbalance.

I attach backup with these skeletons.

In the first file - backup up.

In the second - after

On the stairs up, we leave from the door, we pass small river, and they appear on the trees.