PHP preg_grep() throws a notice when passed array

stupid.php

/**
 * This is my array, let's call him larry
 *
 *  array(1) {
 *    ["canvas-snake"]=>
 *    array(5) {
 *      ["name"]=>
 *      string(12) "canvas-snake"
 *      ["server_path"]=>
 *      string(48) "/Applications/MAMP/htdocs/pl/posted/canvas-snake"
 *      ["size"]=>
 *      int(374)
 *      ["date"]=>
 *      int(1339533162)
 *      ["relative_path"]=>
 *      string(9) "./posted/"
 *    }
 *  }
 *
 *
 * A PHP Error was encountered
 * 
 * Severity: Notice
 * 
 * Message: Array to string conversion
 * 
 * Filename: models/posts_model.php
 * 
 * Line Number: 70
 */

/**
 * pretty urls
 */
$ugly_dirs = preg_grep( '/[A-Z]\S/', $larry );

if( ! empty( $ugly_dirs ) )
{
    /**
     * Note: the code in here *does* run and does work, it's just preg_grep
     * doesn't like larry... poor larry
     */
    foreach( $ugly_dirs as $dir )
    {
        rename( $root . $dir['name'], $root . $this->_format_url( $dir['name'] ) );
    }
}

Did you ever figure out why this is happening? It sounds like a PHP bug.