Cannot remove Overridden Setting for a content type

Problem/Motivation

Cannot remove Overridden Setting for a content type

Steps to reproduce

Go to admin/config/content/node_revision_delete
click Configure for an overridden content type
go to Publishing options tab
unset Delete options (radio button grey)
save
(goes back to prev page)
Setting still Overridden.
Not sure if content type will be included as all custom options are off, or will be using the default values

Proposed resolution

Reset Setting if a content type has no custom values set

Remaining tasks

User interface changes

API changes

Data model changes