Please see also bug 10306 and dependencies. In Koha we are using kohafield in auth_subfield_structure only for the link between authid and 001, as well as authtypecode and 942a. We do not have any further "kohafield functionality" as on the biblio side for additional fields like title, author, etc. (There is no authority counterpart for transform marc to koha, etc.) Sub GetAuthMARCFromKohaField is only called a few times (once in AuthoritiesMarc.pm and twice in authorities.pl). In e.g. SearchAuthorities, GuessAuthid, AddAuthority, etc. 001 is hardcoded. This actually means that you should really NEVER change the "kohafield" mapping in the Subfield structure of Admin/Authority types for 001 and 942a. I would propose here to disable the kohafield for editing on the subfield structure form (just as on bug 19096), and at least add some comments to GetAuthMARCFromKohaField.
*** Bug 31704 has been marked as a duplicate of this bug. ***