ansible group position bug when inventory is yml

hosts.ini

[my_group]
host-1
host-2
host-3

hosts.yml

all:
  children:
    my_group:
      hosts:
        host-1:
        host-2:
        host-3:

playbook.yml

---
- hosts: my_group
- hosts: my_group[0]
- hosts: my_group[1]
- hosts: my_group[2]

run_ini.sh

#!/bin/sh
ansible-inventory -i hosts.ini --graph all
ansible-playbook -i hosts.ini playbook.yml --list-hosts

run_yml.sh

#!/bin/sh
ansible-inventory -i hosts.yml --graph all
ansible-playbook -i hosts.yml playbook.yml --list-hosts