Jetpack contact form not working with do_shortcode()

I was able to implement a solution for forcing the subject line to be what I want it to be (in this case, the title of the post on whose template file I am placing the contact form).

First, hook the custom subject function into the Grunion Contact Form filter:

add_filter('contact_form_subject', 'product_contact_subject');

Now, the function:

function post_contact_subject($subject) {
	$url = $_SERVER['HTTP_REFERER'];
	//Create an array divided by the base url. This example assumes that the post slug immediately follows the root domain. Change this to match your permalink structure.
	$arr = explode(get_site_url() . '/', $url);
	//Make sure that the array has at least two elements.
	if (count($arr) < 2)
		return $subject;
	//Get the slug and remove the query string and any trailing slash if it exists.
	$slug = str_replace('/', '', $arr[1]);
	$slug = preg_replace('/\?.*/', '', $slug);
	//Get the post id based on the slug.
	$id = slug_to_id($slug);
	//title
	$title = get_the_title($id);
	//Return the custom title
	return $title;
}

Now, the function for getting a post’s ID from its slug:

function slug_to_id($slug, $type = 'post') {
	$args=array(
	  'name' => $slug,
	  'post_type' => $type,
	  'post_status' => 'publish',
	  'showposts' => 1,
	  'caller_get_posts'=> 1
	);
	$my_posts = get_posts($args);
	if( $my_posts ) {
		return $my_posts[0]->ID;
	} else {
		return 0;
	}
}

I hope that this helps anybody else with this problem.