The Base is the Problem:

    'base' => add_query_arg('listpostspage','%#%'),

Here ist the full code:

    $pagination_args = array(
        'base'            => add_query_arg('listpostspage','%#%'),
        'format'          => '?listpostspage=%#%',
        'total'           => $the_query->max_num_pages,
        'current'         => $paged,
        'show_all'        => false,
        'end_size'        => 1,
        'mid_size'        => 2,
        'prev_next'       => true,
        'prev_text'       => __( 'Zurück', 'Theme' ),
        'next_text'       => __( 'Weiter', 'Theme' ),
        'type'            => 'plain',
        'add_args'        => false,
        'add_fragment'    => ''
    );

Thanks goes to [raison][1] over at stackoverflow who posted this [answer][2].


  [1]: https://stackoverflow.com/users/2468603/raison
  [2]: https://stackoverflow.com/a/20549327/2593099