The setting "Export new or updated grades only" in the gradebook export xml format is only handled in the preview, not in the file.

To reproduce:

1. Go to the gradebook in a course with some graded activity
2. Be sure to have an ID for each activity and for the course category in the gradebook
3. In the export section, select the XML format
4. Be sure to select "Export new or updated grades only"
5. Click Submit
6. The preview will only show the new or updated grades as expected
7. Click Download

Expected result: The exported file should only contain new or updated grades.

Actual result: The file will include all grades, not only the new or updated grades, which is wrong.