Nailgun validates hidden setting groups

Steps to reproduce in Fuel UI:

1. create an environment (default wizard settings)
2. go to Settings tab, OpenStack Services subtab
3. check "Install Ceilometer and Aodh" and "Use external Mongo DB" settings, "External MongoDB" setting section should appear on the screen
4. input in an invalid value into "MongoDB hosts IP" field to raise a validation error on UI (in my case the field was autocompleted with "admin" value, see the attached screenshot)
5. uncheck "Install Ceilometer and Aodh" and "Use external Mongo DB" settings. "External MongoDB" setting section should disappear from the screen and validation error should not be shown as well as the section was closed.
6. check "Install Sahara" checkbox to enable "Save Settings" button
7. click "Save Settings" button to save the change

Expected result: the change is saved successfully, no error occurred.

Actual result: there is a Nailgun error, PUT /api/clusters/5/attributes failed with 400 Bad Request and the response: {"message": "[hosts_ip] Invalid hosts ip sequence", "errors": []}

The following data was sent to Nailgun http://paste.openstack.org/show/cVKQFEYSmmMg6Ncqo1UR/

Looks like Nailgun validates values in hidden sections, like "External MongoDB" in the case.