API - /groups/issues behaves differently that in API doc

Summary

while we was implementing some feature throughout the Gitlab API, i found, that API call behaves differently, than described in doc, here is our API call:

https://<url>/api/v3/groups/8/issues?labels=customer-related&private_token=<token>&per_page=50&pagination=0

That API call should return all issues - opened and closed. From the doc - state string no Return all issues or just those that are opened or closed.

Why am i think it behaves wrong? Let me explain.

Here is API call with &state=opened:

https://<our-url>/api/v3/groups/8/issues?labels=customer-related&state=opened&private_token=<token>&per_page=50&pagination=0

It returns 39 issues.

Here is API call with &state=closed:

https://<our-url>/api/v3/groups/8/issues?labels=customer-related&state=closed&private_token=<token>&per_page=50&pagination=0

It return 4 issues.

Expected behavior

I think that first API should return ALL issues - 39(opened) + 4(closed)

Actual behavior

This API call return only opened issues.

For our Gitlab/help:

GitLab Community Edition 8.10.3 131ea30b