hello,
A bit late may be but I think you are having the issue because the filter hook is changing the class value before sending it to the browser.
I wanted to change the class as well for the form tag and got the same issue.
But if you change the line that calls the filter in contact-form-7/include/classes.php like this:
`$class = apply_filters( ‘wpcf7_form_class_attr’, ‘class-you-want’ );
This modification did the trick for me…
Hope this help
