Hi, there is the required span missing. Look at the original WP e-mail field:
<p class="comment-form-email"><label for="email">Emailová adresa <span class="required">*</span></label> <input id="email" name="email" type="text" value="" size="30" aria-required="true"></p>
In contrary, you have only:
there definitely should be this:
to keep the WP standard, because CAPTCHA input field IS required. Also, it seems there is the
aria-required="true" attribute missing in the input tag (although I am not aware what such a typo-looking attribute does :)
Could you fix it, please?