[Koha] Using a staff member as a guarantor for a child

Hi there, Is it possible to select a staff member as a guarantor? In the add new patron screen, in the guarantor section, the "set to patron" function works fine when searching for an ordinary member to be the patron, (ie the search patron window returns a result) but it does not find an existing 'staff' member whom I know is in the database. Is this a bug or is it by design? cheers Joann Ransom.