[Revo] modx->toJSON Bug?

<?php
$settings = array(
    'parentId' => 31,
    'thumbWidth' => 110,
    'thumbHeight' => 110,
    'thumbSpacingX' => 12,
    'thumbSpacingY' => 12,
    'thumbBorder' => 3,
    'bigWidth' => 1024,
    'bigHeight' => 1024,
);

$modx->regClientStartupScript('http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js');
$modx->regClientStartupScript('http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/jquery-ui.min.js');
$modx->regClientStartupScript('assets/components/ggViewer/ggViewer.js');

include_once ($modx->getOption('core_path') . "components/gallerygear/gallerygear.class.php");
$gg = new GalleryGear();

$data['settings'] = $settings;

foreach($gg->getPhotos($settings['parentId']) as $photo) {
    $thumb = $photo->setResizedPhoto('crop', $settings['thumbWidth'], $settings['thumbHeight']);
    $big = $photo->setResizedPhoto('fullShrinkOnly', $settings['bigWidth'], $settings['bigHeight']);

    $data['photos'][] = array(
        $thumb->getWebURL(),
        $big->getWebURL()
    );
}

return '<ul class="ggViewer">' . json_encode($data) . '</ul>';
?>