CKEditor Plugin settings vertical tab not showing when isEnabled() is set to TRUE

My Wysiwyg Linebreaks module was working as of 8.x-alpha3—when a user visited admin/config/content/formats/manage/basic_html with a standard profile install, the user would see a 'Conversion Method' configuration form in the 'CKEditor plugin settings' area, regardless of what buttons were enabled.

Now, however, the Conversion Method form/vertical tab is always hidden, no matter what the value returned by isEnabled() (the markup is present, but it is set to display:none). The only way to get the configuration form to display is to add a button (which is really annoying, because it would have to be a non-functional 'dummy' button).

I was under the impression that CKEditorPluginContextualInterface::isEnabled was supposed to allow plugins to display configuration forms with or without buttons, and indeed, that was the case up until sometime in the past couple of months.