Prevent OX to send invitations on iCal import

i have a lot if ics-exports which i need to reimport into OX.
Unfortunatley OX sends each attendee a new invitation wich must not happen.

I tried already to setup both, the old and the new server in emclient/caldav and moved the appointments via drag and drop from old to new and even this causes OX the resend the inivitations.

How can i disable sending these invitations on import?