Hi Bodo,
If you have a look at the top of the page you'll see a description of the CSV structure, when you change the name of a field it disappears from the list, this is because its no longer selected (as the name has been changed). Just click in the box again and the new name will appear in the list - it will have been selelcted with the new name.
hope this solves it!
cheers,
George.