When you can't submit the question for any reason (ie: must include tag), and you fix the issue and click "Ask your Question" again, you are prompted with the human verification captcha
The Human Verification is just that. To confirm that you are a human and not a bot. Most automated process will continually post until they are successful. Ie. They will keep adding tags until the submission is accepted. This is the reason the Trilogy does not contain SPAM. Considering the irritation of spam on other forums and group I am more then happy with this.
This is not a bug, and I am extremely surprised Jeff didn't flag it by-design.
This one bugs me too. I'd suggest if the failure is just a lack of title or tags, that the system skip the CAPTCHA.