Just tested it by trying to register on my forum, everytime you enter the answer it like just dissapears completely everytime.. it dosent work and wont let members join.
That's intentional. The CAPTCHA is intended to be submitted along with the rest of the form, and can only be checked once before being invalidated. If it were checked with AJAX before the form is submitted, it would have to generate a whole new question, rendering the answer pointless.