wp_insert_post not working

Okay, so I have a form that submits a post from the front-end
the code for submitting looks like this:

$post = array(
	'post_author'   => $userdata->ID,
	'post_title'	=> $title,
	'post_category'	=> $category,
	'tags_input'	=> $tags,
	'post_status'	=> 'publish',
	'post_date' 	=> date('Y-m-d H:i:s'),
	'post_date_gmt' => date('Y-m-d H:i:s'),
	'post_type'	=> 'post'
);
$post_id = wp_insert_post($post, false);
if($post_id != 0)
{
	wp_redirect(get_bloginfo('url')."/?p=$post_id");

}else{
	die('error');
}

Problem is that some times it is returning an ID and redirecting to the post only that the post was never actually created. For instance if a post is submitted twice.

I checked the codex and it says that it should only return the post ID if it was inserted into the database?

And before anyone ask the only plugins I have are Akismet and WP-Optimize