Confirmation not working?

I have the pro version.

I have set up a personality test collecting user data (e-mail) before showing the result. I have selected “Ask confirmation” and added a label (and made sure “Optional” is not checked) but when submitting the form the confirmation checkbox is not required and the form is submitted with the confirmation unchecked. If the e-mail field is empty an error is shown and the results are not displayed; the same doesn’t happen with the confirmation checkbox.
I need that confirmation checkbox to be mandatory.

I tried looking for it myself, but with no luck. The relevant javascripts (assets/common/…) are unreadable, and the ajax file that is called when submitting (controllers/quiz-session/class-ajax-save-result.php) didn’t tell me much.

Any suggestion?