Empty meta-box returns publishdate if no value is set?

Question

I have no idea why this would/could happen.

I have a custom metabox for an "event_end_date" set for a custom-post-type. If I leave this field blank it always puts out the publish-date of the post itself?

I use the Custom-Metaboxes-and-Fields-for-WordPress library like this …

$meta_boxes[] = array(
    'id'         => 'event_info_optional',
    'title'      => 'Optional',
    'pages'      => array( 'wr_event'),
    'context'    => 'normal',
    'show_names' => true,
    'priority' => 'core',
    'fields'     => array(

        array(
            'name' => 'End time of event',
            'id'   => $prefix . 'event_end_time',
            'type' => 'text_time',
        )
    ),
);

And I save the value like this …

$wr_event_end_date = isset($_POST['wr_event_end_date']) ? $_POST['wr_event_end_date'] : '';
$event_end_date = new DateTime($wr_event_end_date);
update_post_meta($post->ID, "event_end_date", $event_end_date->getTimestamp());

And I query the value like this …

function get_event_end_date($post) {
   $date = get_post_meta($post->ID, 'event_end_date');
   if ( !empty( $date[0] ) ) {
       //only if a value is saved I return the value
       return $date[0];
   }
}

This works for all other custom fields. Just for my event-end-date it doesn't. If I leave the field empty in my backend and save the post, the post itself always shows the publish-date of the post as event-end-date.

Why and how could this get_event_end_date() function return the publish-date of the post if I leave it empty. If I set a value to the field it works fine, but if I leave it empty I don't want the function to return anything.

UPDATE

        // End-event-date
        /*$wr_event_end_date = isset($_POST['wr_event_end_date']) ? $_POST['wr_event_end_date'] : '';
        $event_end_date = new DateTime($wr_event_end_date);
        update_post_meta($post->ID, "event_end_date", $event_end_date->getTimestamp());*/

        if ( isset($_POST['wr_event_end_date']) ) {
            die('this is getting called even though the field is submitted blank');
            $event_end_date = new DateTime($_POST['wr_event_end_date']);
            update_post_meta($post->ID, "event_end_date", $event_end_date->getTimestamp());
        } else {
            update_post_meta($post->ID, "event_end_date", "");
        }

Answer 1

I'm half asleep here so correct me if I am wrong here but it looks to me like you are saving the publish date of the post each time you save the post,

$wr_event_end_date = isset($_POST['wr_event_end_date']) ? $_POST['wr_event_end_date'] : '';
$event_end_date = new DateTime($wr_event_end_date);
update_post_meta($post->ID, "event_end_date", $event_end_date->getTimestamp());

This -> $event_end_date->getTimestamp() being the culprit.

So regardless of your variable $wr_event_end_date value being set or not, your meta value is being assigned via getTimestamp() because firstly there is no conditional statement that checks for the existence of your,

$_POST['wr_event_end_date'] 

which if FALSE will instead revert to '' (no value) which is then passed to your

new DateTime($wr_event_end_date);

Secondly, because

new DateTime( //is now empty here );

your

getTimestamp()

returns the current time stamp of the post.

UPDATE

You should still use the text_date custom field, example:

array(
    'name' => 'Test Date Picker',
    'desc' => 'field description (optional)',
    'id'   => $prefix . 'test_textdate',
    'type' => 'text_date',
),

...instead of using a timestamp especially if you have no reason to use a timestamp other than to convert it back to a regular date format because WordPress has inbuilt functions for handling date and time formatting.

Here is an example;

global $post;
$text = get_post_meta( $post->ID, '_cmb_test_textdate', true );
$text = date('d F Y', $text); 
echo $text;
    //prints 25 September 2012 for example

I've made sure to test this library to ensure it is in fact outputting results correctly and it sure is.