Commenting inconsistencies

Our new lab blogs process comments quite differently.  On this blog and on Shoe Science, you just click 'post comment' (after entering your comment in the box) and it appears on the blog.  On No DNA Control and RY's blog, clicking 'post comment' gets you a message that your comment could not be posted.  Then you try clicking 'preview comment' and a preview window appears, along with a captcha (one of those word-recognition tests) to complete.  Then when you click 'submit comment' your comment appears.  I wonder if it's the captcha that creates the problem - I'll need to test this on another computer because after posting one comment the problem has disappeared.