Which could lock some users out permanently if the root user was the only user they knew the password to.

It's impossible to have full-disk encryption with that config, right? (i.e., does FileVault work for the root user?)

If you can get in from an install CD, you can reset passwords as needed.

If I were writing this patch, I'd probably check to see if the root user's password was indeed blank, but given that use of the root account only is extremely unsupported I cannot get too upset about Apple breaking that use case as long as you can get back in.

The issue wasn’t actually specific to a blank password. You could try to log in as root using any password, and as long as root had never had a password set, it would fail but set root’s password to whatever you entered.