function render_posttitle( $form_id, $post_id, $form_settings ) {
    $value = get_post_meta( $post_id, 'post_title', true );
    update_post_meta( $post_id, 'meta_posttitle', $value );
    ?>
    <div class="wpuf-fields">
        <input type="hidden" name="my_posttitle" value="<?php echo esc_attr( $value ); ?>">
    </div>
    <?php
}
add_action( 'hook_render_posttitle', 'render_posttitle', 10, 3 );

/* Write meta key */
function get_posttitle( $post_id ) {
    if ( isset( $_POST['my_posttitle'] ) ) {
        update_post_meta( $post_id, 'meta_posttitle', $_POST['my_posttitle'] );
    }
}

add_action( 'wpuf_add_post_after_insert', 'get_posttitle' );
add_action( 'wpuf_edit_post_after_update', 'get_posttitle' );