We enabled Communities in our production environment, and now, non-admin users are reporting they see this new black header at the top of Salesforce. I believe this bar is called the "Global Header":
While trying to figure out how to get rid of this thing, I found articles on the web (salesforce.com) on how to enable this header using permission sets, but have not found a way to disable it.
Strange that it turns on for non-admin (plus admin) users by default. I would think that would something one would want to explicitly enable.
Per request of glls, we are not yet using any templates. We simply enabled the Lightning Communities feature.