Widget dropdown always displays first option

Question

I have a custom widget that I have made but whenever I change the dropdown value it always reverts to the first option when I save the widget. How can I have it display whatever option the user selects?

  // update widget
  function update($new_instance, $old_instance) {
        $instance = $old_instance;
        // Fields
        $instance['category'] = strip_tags($new_instance['category']);
       return $instance;
  }

  // widget form creation
  function form($instance) {
    // Check values
    if( $instance) {
         $category = esc_attr($instance['app_category']);
         $instance['category'] = strip_tags( $new_instance['category'] );
    } else {
         $category = '';
    }
    //Set up some default widget settings.
    $defaults = array( 'category' => '');
    $instance = wp_parse_args( (array) $instance, $defaults );
?>
    <!-- Category Select Menu -->
    <p>
      <label for="<?php echo $this->get_field_id('category'); ?>"><?php _e('App Category: ', 'AppManager_plugin'); ?></label>
      <h1><?php echo $category ?></h1>
      <h1><?php echo $instance['category'] ?></h1>
      <select id="<?php echo $this->get_field_id('category'); ?>" name="<?php echo $this->get_field_name('Category'); ?>" >
        <?php foreach(get_terms('app_category','parent=0&hide_empty=0') as $term) { ?>
          <option <?php selected( $instance['category'], $term->term_id ); ?> value="<?php echo $term->term_id; ?>"><?php echo $term->name; ?></option>
        <?php } ?>
      </select>
    </p>

Answer 1

I got an answer on WordPress Support forms, http://wordpress.org/support/topic/widget-dropdown-always-displays-first-option?replies=6

Replaced function form with,

function form( $instance ) {
    // Check values
    $category = isset( $instance['category'] ) ? (int) $instance['category'] : '';
    $terms = get_terms( 'app_category', 'parent=0&hide_empty=0' );
    if ( !empty( $terms ) && !is_wp_error( $terms ) ) {
?>

And changed,

name="<?php echo $this->get_field_name( 'Category' ); ?>"

to

name="<?php echo $this->get_field_name( 'category' ); ?>"