Sometimes captcha doesn't work properly. And times no need to complete captcha. But Bitcointalk security is very advanced level don't worry about it.
You just need to check all the boxes and they work fine verifying you but as you said no need to complete captcha then it might be the case when you have permanently logged in your account from any device that will bypass it otherwise if you login each time you will have to solve the captcha to login into your account.Captcha are different from the security and you must also take necessary steps for your account safety.