A bug in ansible?

my_inventory

localhost inventory_variable=true ansible_connection=local

playbook.yml

---
- name: Testing Issue
  hosts: all
  pre_tasks:
    - debug: var={{ item }}
      with_items:
        - inventory_variable
        - playbook_variable
  roles:
    - role: role1
      playbook_variable: "{{ inventory_variable | default(false) }}"

roles-role1-tasks-main.yml

---

- name: Test Playbook Variable
  debug: var=playbook_variable

ansible-playbook -i my_inventory playbook.yml

PLAY [Testing Issue] **********************************************************

GATHERING FACTS ***************************************************************
ok: [localhost]

TASK: [debug var={{ item }}] **************************************************
ok: [localhost] => (item=inventory_variable) => {
"item": "inventory_variable",
"var": {
"inventory_variable": "true"
}
}
ok: [localhost] => (item=playbook_variable) => {
"item": "playbook_variable",
"var": {
"playbook_variable": "playbook_variable"
}
}

TASK: [role1 | Test Playbook Variable] ****************************************
ok: [localhost] => {
"var": {
"playbook_variable": "False"
}
}

PLAY RECAP ********************************************************************
localhost : ok=3 changed=0 unreachable=0 failed=0