[Koha] Problem with saving changes to MARC records

Hello, I have a problem with saving corrections in MARC records imported to our catalog. During importing through Z39.50 all the changes done to record, like framework and filling of empty fields or changing them, I can save and they stay as I wish them to be. But when I go to the record next time, saving of corrections is not possible. I can only change the framework then but all the corrections done to MARC fields disappear. What could it be a reason? Med vänlig hälsning Lukasz Mesek Vuxenbibliotekarie Alingsås bibliotek lukasz.mesek@alingsas.se