Required field validation not working.

Hi
I have some required fields that are hidden, when the user submits the form while the required fields are hidden all the fields display asking for input. The validation doesn’t seem to work. I’ve created a simple form to illustrate this. You see the from at this URL https://mandrelbends.co.uk/form-testing/

<label> Your Name (required)
    [text* your-name] </label>

<label> Your Email (required)
    [email* your-email] </label>

<label> Subject
    [text your-subject] </label>

[checkbox checkbox-552 "yes"]
[group group-603]
<label> Your Message
    [textarea* your-message] </label>
[/group]

[submit "Send"]