That's a bit meta, a bit stackoverflow question - what's the point of asking a CAPTCHA challenge to a user that's already replied the CAPTCHA question properly?
I've been giving several short answers on SO and I got the time limit throttle. I kept pressing "submit" because I didn't know whether the three minutes had already passed or not and pretty often I would get challenged by the CAPTCHA.
Even after replying to it correctly, I got another CAPTCHA question next time I rushed the "submit" button. Why is it made this way?