Win2012R2, ProGet 6.0.11 Free is hosted as IIS application.
Preview of the new Security Management behaviors and UI is turned on.
Active Directory (LDAP) enabled for current domain only without additional settings.
You may see "Although LDAP / Active Directory is enabled, this feature is not available in ProGet Free. Use your Built-in Directory Username and Password to log-in." message when you tried to logon.
But you able to logon with domain credentials.

I tried to reproduce it with docker image with no luck.

Is it bug or this is new feature of "new Security Management"?
I suppose it is bug related to windows implemenation (dev team is concentrated on docker images) and will be fixed in next versions?