[afiler]

Even on El Capitan, I was able to unlock with "root" on my first try. From there, I could add a new admin user. This seems... not good.

[joshvm]

I wasn't able to do it on 10.12.6 (Sierra) though, so perhaps there's something else odd here?

[uuuuuuuuuuuu]

Doesn't work for me either on 10.12.6.

[cthalupa]

I cannot reproduce this on Sierra or El Cap

[eridius]

The bug does not exist on El Capitan. Your description tells me you already had the root user enabled with no password (which is something you can do with Directory Utility.app)

[JustSomeNobody]

Especially not good is Apple likely won't fix it in El Cap. They'll tell all of us to upgrade. I don't want that buggy HS mess.

[jobu]

When I tried to make a new user after unlocking as "root" it ended up making a group instead. (High Sierra 10.13.1)