[Koha] Cannot keep changes in MARC framework for Authority MARC Framework: PERSO_NAME Framework

Dear all, Somehow I seem to be unable to keep changes to the Personal Name authority's MARC Framework. I was trying to the set the "repeatable" field to the 100 Tag (HEADING--PERSONAL NAME) by editing the MARC framework in Administration->Authority Types, but after submitting my changes to the field are gone. What am I doing wrong? (Working with Koha 3.00.00.107) Appreciating any hints and suggestions, Best regards, Marc