Cannot spawn mobs riding other mobs with the new EntityTag on eggs

As the title says, you can't spawn mobs riding other mobs with the spawn eggs and their new item tag for entities.

/give @p spawn_egg 1 0 {EntityTag:{id:"Creeper",Riding:{id:"Spider",CustomName:"Bob"}}}

Spider doesn't show up.

This is possibly linked to every other issue about the new tag, such as the baby mob issue.