Client side mform validation ignored in the Boost theme

Steps to reproduce

1. Prepare a feedback with Numerical question on the first page (set as required) and Short text answer on the second page (also set as required).
2. As a student, start answering the feedback.
3. Without filling a value into the fields, attempt to navigate to the next page or submit the feedback.

Expected result: Client side navigation should display the "Required" warning and the actual page reload should be cancelled (works like that under the Clean theme)

Actual behaviour: The "Required" warning is displayed, yet the browser still reloads the page which triggers the server-side validation. Notice the console error.

It seems to be Feedback specific as text fields validation normally works elsewhere.