Removing a face, then adding a new one (in add-on prefs) causes deletion of other 'face' headers

[JohnDDuncanIII]

ex: mail.identity.id15.headers;xface,xface2,face gets renamed to mail.identity.id15.headers;xx2,face'

this affects the users 'extra' headers that are sent. If they are only using one header, or multiple headers w/o the word 'face' in them, then there is no problem.

TODO: better regex