Its noted that whenever a Mail account is deleted from iOS Settings/Mail, Contacts, Calendars the screen refreshes and arbitrarily duplicates Mail accounts onscreen.
To get the accurate view of your Mail accounts, you have to exit the Mail, Contacts, Calendars’ pane by selecting any other Settings pane, e.g. Safari, and re-select the Mail, Contacts, Calendars pane again.
This behaviour has been noticed since iOS 8.1.1 and has yet to be addressed and persists into 8.1.2.
Feedback has been sent into Apple to request a fix. If you notice the same phenomenon, send your fix request to Apple today at Apple’s Feedback page.
If you know a fix, please leave a comment.