`can_create_group` default setting not respected


I am testing ldap integration with gitlab omnibus. I encountered a strange problem regarding the setting default_can_create_group in gitlab.rb. I set it so false. Despite that, new users logged in via ldap can still create groups.
I wrote a little summary on stackoverflow. But it seems this is a better place to ask this. So if anyone has any suggestions, I am up for it.
Another thing is, that I cant reset the can_create_group flag via the rest API. It returns a 200 but it does not set the setting… Seems like a bug to me, but I want to make sure I asked everywhere, before filing one.
Here is the link to the stack overflow question, which describes the problem with a little more detail:

I experienced the same problem with GitLab Community Edition 8.7.2.
At the moment I found a workaround changing line 100 in file 1_settings.rb
Settings.gitlab[‘default_can_create_group’] = true if Settings.gitlab[‘default_can_create_group’].nil?
Settings.gitlab[‘default_can_create_group’] = false

After restart, new users can not create group by default.