CLFMAS overwrite existing class data

I Use the CLFMAS IDOC to update class data in SAP. I maintain the data in MDM and uses and IDOC CLFMAS to post the new data in SAP. My problem is that "old class data is lost". I have tried to change the MSGFN to different values, but I still get the same problem.

Do anyone have an idea how to solve this?

Regards

John-Kjell