gistfile1.txt

---
- hosts: localhost
  user: belisarius
  vars:
    test:
      - [ "uid", ["val1","val2"]]
      - [ "uid2", ["val1","val2"]]
  tasks:
    - debug: msg="{{ test }}"
    # result is :
    # "msg": "[['uid', ['val1', 'val2']], ['uid2', ['val1', 'val2']]]"

    - debug: msg="{{ item }}"
      with_items: test
    # expected result is :
    # "msg": "['uid', ['val1', 'val2']]"
    # "msg": "['uid2', ['val1', 'val2']]"

    # real result is :
    # "msg": "uid"
    # "msg": "['val1', 'val2']"
    # "msg": "uid2"
    # "msg": "['val1', 'val2']"
}