This has bugged me for a while.
Add this in place of line 844 of /grade/lib.php
$title = $element['object']->get_name();
$header .= $title;
And this in place of line 865:
$header = '<a href="'.$url.'" title="'.$title.'">'.$header.'</a>';
- has been marked as being related by
MDL-13960 Make full use of title attributes in the gradebook