Build time ARG does not take value from command line

In my Dockerfile I declare an ARG: ADMIN_PASSWORD, when I do $docker build --build-arg ADMIN_PASSWORD=value1, the ARG remains blank. I know it is not a good practice to pass secrets as an ARG, I experimented and changed the ARG name to ADMIN_MNG and it took the value passed in.
Is there a new feature in Docker where if the ARG name has the string “PASS” or “PASSWORD” it will not take the value?
I run Docker 17.05.0-ce, the behavior is also reproducible in Docker 1.12.6.