addons/captcha/captcha.addon.php에서 

// compare session when calling actions such as writing a post or a comment on the board/issue tracker module

if(!$_SESSION['captcha_authed'] && in_array(Context::get('act'), $target_acts))

{

Context::loadLang('./addons/captcha/lang');

$ModuleHandler->error = "captcha_denied";

}

이곳을

// compare session when calling actions such as writing a post or a comment on the board/issue tracker module

if(!$_SESSION['captcha_authed'] && in_array(Context::get('act'), $target_acts))

{

Context::loadLang('./addons/captcha/lang');

$_SESSION['join_extend_authed'] = true;

$ModuleHandler->error = "captcha_denied";

}

로 바꿔주세요.