[Bug] Inconsistent return value from task_positions endpoint

[charignon]

When I request the list of tasks in a list with the tasks API endpoint and requests the task positions in a list with the task_position endpoint, for some lists I get a different set of ids.
The web UI and the app shows the tasks from the tasks endpoint.

Here is the minimal repro case with anonymized ids:

$ curl -s -H "X-Access-Token:XXX" -H "X-Client-ID:YYY" "https://a.wunderlist.com/api/v1/task_positions?list_id=123"  | jq '.[0].values'
[
  5,
  1,
  2
]

$ curl -s  -H "X-Access-Token:XXX" -H "X-Client-ID:YYY" "https://a.wunderlist.com/api/v1/tasks?list_id=123" | jq ".[].id"
1
2
3

Note: this breaks https://github.com/myuhe/org-wunderlist.el.