I have a similar situation but it’s not caused by an old database, rather old code and a new database.

I just created a new WP site. I installed Piklist version 0.9.9.15. I am using a meta-box to define a row with 3 columns or “features.” Each feature has a headline, image, text.

piklist( 'field', array(
   'type' => 'group',
   'field' => 'panel_features',
   'label' => 'The three features for this panel',
   'description' => 'Enter content for features. The quantity should be a multiple of 3.',
   'columns' => 12,
   'add_more' => true,
   'fields' => array(
      array(
         'type' => 'text',
         'field' => 'feature_headline',
         'label' => 'Headline',
      ),
      array(
         'type' => 'file',
         'field' => 'feature_image',
         'label' => 'Select Image',
         'options' => array(
            'modal_title' => 'Add Image',
            'button' => 'Add',
         ),
      ),
      array(
         'type' => 'editor',
         'field' => 'feature_text',
         'label' => 'Text',
         'options' => array (
            'media_buttons' => false,
            'textarea_rows' => 3,
            'teeny' => true,
            'quicktags' => true,
         ),
      ),
   ),
));

This meta-box code is in a little plugin I created and is in use on several websites. I just copied the plugin to the new website and configured 3 features. But the images didn’t show up on the new site. I used piklist::pre and looked at the data. It looks fine but note that each image is a single ID, not an array:

Array
(
    [0] => Array
        (
            [feature_headline] => Feature 1
            [feature_image] => 14195
            [feature_text] => Text for Feature 1.
        )

    [1] => Array
        (
            [feature_headline] => Feature 2
            [feature_image] => 14194
            [feature_text] => Text for Feature 2.
        )

    [2] => Array
        (
            [feature_headline] => Feature 3
            [feature_image] => 14191
            [feature_text] => Text for Feature 3.
        )
)

But my code, which is working with the above fields on several existing websites, expects an array:
$image = wp_get_attachment_image( $feature['feature_image'][0], $image_size, false );

When I added a second image to one of the features, it replaced the feature image instead of being added to an array.

In fact I prefer the new behavior because the file sub-field is not an add-more so it feels more correct and is simpler. My concern is that it is a change from previous behavior and I’m really concerned that old sites are going to break. Should I run a conversion on the old sites? Do I need to go back and edit code?

Thanks!
Donna

My problem was resolved with the release of v 0.9.9.16.