On MARC Framework modification (/cgi-bin/koha/admin/marctagstructure.pl) : - search for a specific tag, for example '800' - 'Edit tag' - save it, with or without modifications - note you're search for '800' is still active - 'Edit tag' again - cancel - boum ! you're back to tag 000 Behaviours should be more consistent, I think the search should be kept (personally, I often select 'Edit tag' instead of 'Edit subfields', and this bug can easily be annoying...).