Widget dropdown always displays first option

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' ); ?>"