Using Captcha with Multichoice Question

Has anyone implemented Captcha with a multichoice question? The captcha is working fine on a standard form - ie user login form. When I try to add it to a quiz question, using the form id quiz_question_answering_form, the captcha appears but the user can bypass without answering the captcha. I've tried multiple implementations - math, css, draggable, unrelated word - all show the same behvaior.

I'm stumped, any suggestions?

Thanks!