[Plugin: Boom Captcha] Captcha not entirely working

The captcha isn’t entirely working on my site. I checked these checkboxes:

Enable for comment forms
Enable for logged in users
Enable for loggin form

When I test posting a comment logged in as a registered user it works.
When I log in it works too.
But when I test it as a non-logged user it doesn’t work. I don’t see the captcha in the form but when I hit the send button a message appears saying “Captcha code is incorrect”.

Any ideas?

http://wordpress.org/extend/plugins/boom-captcha/