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.
This is a feature.