function meta_release_setup()
{
	global $post;
 
	$release['Album Title'] = get_post_meta($post->ID,'Album Title',TRUE);
	$release['Artist Name'] = get_post_meta($post->ID,'Artist Name',TRUE);
	$release['Label'] = get_post_meta($post->ID,'Label',TRUE);
	$release['Year'] = get_post_meta($post->ID,'Year',TRUE);
	$release['Artist Website'] = get_post_meta($post->ID,'Artist Website',TRUE);
	$release['Tracklist'] = get_post_meta($post->ID,'Tracklist',TRUE);

 	include(TEMPLATEPATH . '/post-meta-release.php');
 
	// create a custom nonce for submit verification later
	echo '<input type="hidden" name="meta_release_noncename" value="' . wp_create_nonce(__FILE__) . '" />';
}
 
function meta_release_save($post_id) 
{
	// authentication checks
 
	// make sure data came from our meta box
	if (!wp_verify_nonce($_POST['meta_release_noncename'],__FILE__)) return $post_id;
 
	// check user permissions
	if ($_POST['post_type'] == 'page') 
	{
		if (!current_user_can('edit_page', $post_id)) return $post_id;
	}
	else 
	{
		if (!current_user_can('edit_post', $post_id)) return $post_id;
	}
 
	// authentication passed, save data
 
	// var types
	// single: _my_meta[var]
	// array: _my_meta[var][]
	// grouped array: _my_meta[var_group][0][var_1], _my_meta[var_group][0][var_2]
    
	foreach ($_POST['release'] as $field => $value):
			$current_data = get_post_meta($post_id, $field, TRUE);	
 			$new_data = $value;
  
		if ($current_data) 
		{
			if (is_null($new_data)) delete_post_meta($post_id,$field);
			else update_post_meta($post_id,$field,$new_data);
		}
		elseif (!is_null($new_data))
		{
			add_post_meta($post_id,$field,$new_data,TRUE);
		}
	endforeach;

	return $post_id;

}

Solution - 1

Hi, Try changing your codes to update only and not check if there is previous value. You function meta release setup should get the previous enter post meta value and fill up the inputs for submission. This way you will not need to check for old value, because it will be posted back if there is no changes. Please try the below codes.

function meta_release_save($post_id) 

{

	// authentication checks

 

	// make sure data came from our meta box

	if (!wp_verify_nonce($_POST['meta_release_noncename'],__FILE__)) return $post_id;

 

	// check user permissions

	if ($_POST['post_type'] == 'page') 

	{

		if (!current_user_can('edit_page', $post_id)) return $post_id;

	}

	else 

	{

		if (!current_user_can('edit_post', $post_id)) return $post_id;

	}

 

	// authentication passed, save data

 

	// var types

	// single: _my_meta[var]

	// array: _my_meta[var][]

	// grouped array: _my_meta[var_group][0][var_1], _my_meta[var_group][0][var_2]

    

	foreach ($_POST['release'] as $field => $value):


 			$new_data = $value;

			update_post_meta($post_id,$field,$new_data,TRUE);

	
	endforeach;

}

Solution - 2

if you need to clear the values when this are empty, my suggestion is to change the current code to:

<?php
function meta_release_save($post_id) 
{
	// authentication checks
	// make sure data came from our meta box

	if (!wp_verify_nonce($_POST['meta_release_noncename'],__FILE__)) return $post_id;

	// check user permissions

	if ($_POST['post_type'] == 'page') 
	{
		if (!current_user_can('edit_page', $post_id)) return $post_id;
	}
	else 
	{
		if (!current_user_can('edit_post', $post_id)) return $post_id;
	}

	// authentication passed, save data
	// var types
	// single: _my_meta[var]
	// array: _my_meta[var][]
	// grouped array: _my_meta[var_group][0][var_1], _my_meta[var_group][0][var_2]
	foreach ($_POST['release'] as $field => $value)
	{
		$new_data = $value;

		if ($new_data != '')
		{
			update_post_meta($post_id, $field, esc_attr($new_data));
		}
		else
		{
			delete_post_meta($post_id,$field);
		}
	}

	return $post_id;
}