wp-postratings thumbnail voting only effects first thumbnail

Question

I have a problem with voting using wp-postratings. I have a overview page with multiple thumbnails and want users to vote on this page. Problem is that the voting on all displayed thumbnails effects only the first thumbnail on this page. I think it has something to do with my query, but can't figure out what. Below my code that I use:

                        <?php
                    $posts = get_posts('posts_per_page=1000&category='. $category->term_id);
                    foreach($posts as $post) :
                    $thumb = get_post_meta($post->ID, 'thumb', $single = true);
                    ?>

                    <?php if (!empty($thumb)) { ?>
                        <li>
                            <?php $thumb = get_post_meta($post->ID, 'thumb', $single = true); ?>
                            <?php $artistnaam = get_post_meta($post->ID, 'artistnaam', $single = true); ?>
                            <?php $drukproefwinnaar = get_post_meta($post->ID, 'drukproefwinnaar', $single = true); ?>

                            <?php if (!empty($drukproefwinnaar)) { ?>
                                <div class="winnaar"></div>
                                <a href="<?php the_permalink(); ?>"><img src="<?php echo $thumb; ?>" class="img" alt="<?php the_title(); ?>" title="<?php the_title(); ?>"width="171" height="171" /></a>
                            <?php } else { ?>
                                <a href="<?php the_permalink(); ?>"><img src="<?php echo $thumb; ?>" class="img" alt="<?php the_title(); ?>" title="<?php the_title(); ?>"width="171" height="171" /></a>
                            <?php } ?>    

                            <div class="corners"></div>                               
                            <a href="<?php the_permalink(); ?>"> 
                            <div class="info">
                                <h3><?php echo $artistnaam; ?></h3>
                                <div class="excerpt"><?php the_excerpt(); ?></div>
                                <div class="currentrating"><?php if(function_exists('the_ratings')) { the_ratings(); } ?></div>
                            </div>
                            </a>
                        </li>
                    <?php } ?>
                    <?php endforeach; ?>
                    <?php endforeach; ?>

Strange thing is, when I use the_ratings_results, it works for all thumbnails....

<?php echo the_ratings_results(get_the_id()); ?>

Might be a wp-postratings problem after all? Anyone got the same problem?