Redmine

I am trying to create ticket with parent ticket.

First of all i am creating parent ticket:

cat $TMPNAM
{
  "issue": {
"project_id": "rugion",
"tracker_id": 5,
"priority_id": 6,
"subject": "TEST ticket",
"description": "test ticket",
"category_id": 90,
"fixed_version_id": 390,
"assigned_to_id": 61,
"parent_issue_id": "28173",
"custom_fields":
[
...skipped...
]
  }
}

curl -k -s -H "Content-Type: application/json" -X POST --data "`cat ${TMPNAM}`" -H "X-Redmine-API-Key: ...skipped..." https://redmine.dev.rugion.ru/issues.json

{"issue":{"id":28181, ....}

Getting this issue.id value i am creating child of this ticket like this:

cat $TMPNAM
{
  "issue": {
    "project_id": "rugion",
    "tracker_id": 5,
    "priority_id": 6,
    "subject": "TEST ticket 2",
    "description": "Test ticket 2",
    "category_id": 90,
    "fixed_version_id": 390,
    "assigned_to_id": 61,
    "parent_issue_id": 28181,
    "custom_fields":
    [
    ...skipped...
    ]
  }
}

curl -k -s -H "Content-Type: application/json" -X POST --data "`cat ${TMPNAM}`" -H "X-Redmine-API-Key: ...skipped..." https://redmine.dev.rugion.ru/issues.json

{"issue":{"id":28182, ....}

As a result i get two tickets without any relations.

I expect that ticket 28182 will be a child of ticket 28181.

PS: It was checked in versions 2.6.0 and 2.6.1.