Wrong result returned in the case of with-items, retry and concurrency

Hi Guys.

In a distributed environment (4 servers with engine/executor on each) we are experiencing issue with the following example workflow:

~~~
---
version: '2.0'

with-items-retry-concurency:
  type: direct

  task-defaults:
    concurrency: 10

  tasks:
    with-items:
      action: std.echo
      with-items: int in <% range(0,20) %>
      input:
        output: <% $.int %>
      retry:
        count: 5
        delay: 3
        continue-on: <% task().result %>
      publish:
        result: <% task().result %>

~~~

Mistral publishes wrong result for some reason:

~~~
[
    0,
    1,
    2,
    3,
    4,
    5,
    6,
    7,
    8,
    9,
    10,
    10,
    11,
    11,
    12,
    12,
    13,
    13,
    14,
    14
]
~~~

In the case of concurrency: 1 the result is OK:

~~~
[
    0,
    1,
    2,
    3,
    4,
    5,
    6,
    7,
    8,
    9,
    10,
    11,
    12,
    13,
    14,
    15,
    16,
    17,
    18,
    19
]
~~~

In the case of concurrency equal to with-items count (20 in the case of example workflow) it is OK too:

~~~
[
    0,
    1,
    2,
    3,
    4,
    5,
    6,
    7,
    8,
    9,
    10,
    11,
    12,
    13,
    14,
    15,
    16,
    17,
    18,
    19
]
~~~

# rpm -qa | grep mistral
python3-mistralclient-3.10.0-0.20190920090831.dc246bf.el8ost.noarch
openstack-mistral-common-9.0.2-0.20191125120837.6651519.el8ost.noarch
python3-mistral-9.0.2-0.20191125120837.6651519.el8ost.noarch
openstack-mistral-engine-9.0.2-0.20191125120837.6651519.el8ost.noarch
python3-mistral-lib-1.2.1-0.20191118120254.4bac2b2.el8ost.noarch
openstack-mistral-event-engine-9.0.2-0.20191125120837.6651519.el8ost.noarch
openstack-mistral-executor-9.0.2-0.20191125120837.6651519.el8ost.noarch
openstack-mistral-api-9.0.2-0.20191125120837.6651519.el8ost.noarch