I think it's just how DW captchas work. As far as I know, they start enforcing captchas after a certain number of comments on a post (4,000, I think?). And the math thing is probably what DW automatically puts there. Not sure if you can change it to something a little less math-y. :-)
Catchpa Rant Post
(Anonymous) 2015-07-07 02:14 am (UTC)(link)Re: Catchpa Rant Post
(Anonymous) 2015-07-07 02:24 am (UTC)(link)The drawback is, if you get the captcha wrong too many times, your comment will misfire.
Re: Catchpa Rant Post
(Anonymous) 2015-07-07 06:44 am (UTC)(link)Re: Catchpa Rant Post
(Anonymous) 2015-07-07 01:39 pm (UTC)(link)