I wanted to delete/empty the configuration setting 'phpmailer.smtp-user' but was unable to. The conf interface tells me it's in the database but locked:

This configuration is locked and can not be edited from the web interface. Use `./bin/config` in `phabricator/` to edit it.

So I do just that:

./config delete phpmailer.smtp-user
Usage Exception: Configuration key 'phpmailer.smtp-user' is not set in local configuration!

Alright, then I'll empty it:

./config set phpmailer.smtp-user ""
Set 'phpmailer.smtp-user' in local configuration.

Wait, local conf? But this setting's value resides in the database (which overrides the local conf). So now I need to fix this manually in the database...

I suspect that this setting was locked some time after I set it using the web interface?