Cannot change binding method

I received a report from a user this morning who was unable to login with his LDAP credentials. I discovered that the LDAP server settings for this module had been changed to Anonymous Bind (4th option), which we don't ever use. I attempted to change it to the 3rd option, but every time I submit the form, it reverts to the 4th option. Here's a quick screencast of that happening.

Logs indicate "LDAP bind failure" for each attempted login.