rwmb_frontend_before_process with ajax enabled not working

Hi,

I was testing the 'rwmb_frontend_before_process' and it seems it does not fire when ajax=true is set in the shortcode? I set ajax=false and I can confirm the 'rwmb_frontend_before_process' does fire correctly. Any ideas?

[mb_frontend_form id="dc-product" confirmation="Your post has been successful" ajax="true"]

add_action( 'rwmb_frontend_before_process', function( $config ) {  
    if ( 'dc-product' === $config['id'] ) {
        error_log(print_r($config, true)); //test
    }   
}, 10, 2 );

Thanks

Nick