Well… I found a temporary work-around by replacing
<?php while (have_posts()) : the_post(); ?>
in the Main Index Template with
<?php $my_query = new WP_Query('showposts=6');
while ($my_query->have_posts()) : $my_query->the_post();
$do_not_duplicate = $post->ID; ?>
This seems to get rid of the ‘Previous Entries’ link though, making it impossible to see older posts…
If anyone has any ideas, then please let me know. Thank you!