I'm trying to delete a content type from SharePoint, but it keeps giving me the message:  

"The content type FOO BAR is part of an application feature."  

I have deactivated the feature, retracted the solution and deleted the package from the solution store, the content type is not in use by any lists (I followed the method [here](http://blog.thekid.me.uk/archive/2008/11/03/a-tip-when-looking-at-the-sharepoint-content-db.aspx)), there are no errors in the logs.

I have also tried to do it through code, with the same result.  

I tried following the advice to change it's settings so that "Update all content types inheriting from this type" is set to "NO", but it won't save/persist that change (no error, it just keeps reverting back to "YES").

How can I delete this content type?