We have just found when editing a course Section Summary ( site-name/course/editsection.php ) the "cancel" button does NOT cancel, it saves instead - the same as "save" button.
This is seen in version 2.4.9 and 2.5.1 that I have tried. Also tested a moodle 2.5.3 which cancels as expected.
I guess the cancel button isn't often used …