elusive recaptcha bug. Copy code always fails

Why this happens:

This happens when the client has JavaScript disabled. Let's take a look at the following sample code.

Example code from reCAPTCHA: Tips and Guidelines API documentation:

<script type="text/javascript"
   src="https://www.google.com/recaptcha/api/challenge?k=your_public_key">
</script>

<noscript>
   <iframe src="https://www.google.com/recaptcha/api/noscript?k=your_public_key"
       height="300" width="500" frameborder="0"></iframe><br>
   <textarea name="recaptcha_challenge_field" rows="3" cols="40">
   </textarea>
   <input type="hidden" name="recaptcha_response_field"
       value="manual_challenge">
</noscript>

As we can see, there are noscript tags containing an iframe, a textarea, and a hidden input. When JavaScript is disabled, it will render the contents of the noscript tags and it will look something like this.

The iframe contains a form where a user can enter the captcha and submit the form, upon which the iframe will load a new page containing the response code. Since JavaScript is disabled, the only way to get that token to the parent page's form is to have the user copy-and-paste the token into the textarea in the example.

Workaround?:

So long as the user correctly copy-and-pastes the token, it should work fine. Double-check that the HTML for the captcha contains the correct fallback elements. You can also disable JavaScript in your browser to test it yourself.