PHP Notice: Undefined index: domain

When attempting to test S3 or S3/cloudfront, I’m getting this error:

PHP Notice:  Undefined index: domain in /var/www/wordpress/wp-content/plug
ins/w3-total-cache/lib/W3/AdminActions/CdnActionsAdmin.php on line 380

This works fine on other 4.0 sites I admin, but this one doesn’t seem to be writing any of it’s config to the database. It seems to be storing it somewhere, though because the config info is still around after deleting / reinstalling the plugin (eg the info is pre-populated in the form fields).

I’ve tried remove, deleting and updating. I’ve also tried disabling all other plugins, setting apc.stat=1 and restarting apache. I’ve even greped through the file system and mysql dumps looking for my s3 bucket name / cloudfront domain. All have come up empty.

https://wordpress.org/plugins/w3-total-cache/