Stylizer dropped machine name

I've been getting the following error message:

Notice: Undefined index: stylizer: in ctools_get_plugins() (line 338 of /srv/bindings/[mysite]/code/sites/all/modules/ctools/includes/plugins.inc).

I did some investigating, and it seems I have a Panel Pane stylizer style that saved, but somehow dropped the machine name, so it has a type, a title, but no name. Trying to edit or delete the item from the Stylizer dashboard just serves up a 404 because the action has no machine name to attach to.

Where can I find the base definitions for these styles so I can delete the broken style at the source? Without a machine name, it's not showing with any of the other styles.