Are you sure you haven't somehow deleted the original field, and then added it again? MC normally appends '(1)' to the name if the field already exists. Then, of course, you would see both [satz] and [satz (1)] in Manage Library Fields, and expressions using [satz] would be unaffected. Try adding [satz] to a list view. If you see nothing for records for which there should be data, that would suggest the data is gone. If so, restore a Library backup.