Teacher is unable to download test results.

How to reproduce:
1. As teacher or admin, click on any test that was completed by at least one student.
2. Click on The Results Grade link.
2. The button "Download table data as" (see http://docs.moodle.org/23/en/File:Quiz_results_grades_report_show_marks.png) is missing. The system shows only text (no hyperlink) instead of it.