Post in multiple categories- get posts excluding one cat

Hello!
I have posts that can be both in category ‘5’ and ‘152’ at the same time.
In right sidebar I have to retrieve posts from category ‘5’ but excluding category ‘152’ from that post listing.
I HAVE A WORKING SOLUTION !!!!!
– now you wonder why am I here then, right? !!! ??
HERE IS MY DILLEMA:
1) Here is the code of a working solution:

<ul>
<?php

$lastposts = get_posts('numberposts=7&cat=5&category__not_in=152');

        foreach($lastposts as $post) :
               setup_postdata($post);
?>

<li>
<a href="<?php the_permalink(); ?>" target="_blank">
<?php the_title(); ?></a>
</li>

<?php endforeach; ?>

</ul>

2) Here is the code that was NOT working, it was displaying posts also from cat=’152′ despite of the exclude ‘cat__not_in’ :

<ul>
<?php
    $args=array(
	'cat' => 5,
	'cat__not_in' => array(152),
	'post_type' => 'post',
        'post_status' => 'publish',
	'order' => 'DESC',
	'posts_per_page' => 5
          );
     query_posts( $args ); ?>

<?php if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

<li>
<a href="<?php the_permalink(); ?>" target="_blank"><?php the_title(); ?></a>
</li>

<?php endwhile; else: ?>
<li><?php _e('No other news.'); ?></li>
<?php endif; ?>

</ul>

Please, for a benefit of a future projects ?? , can a good souls that exists on this forum explain to me WHY OH WHY the method 2) with $args in array won’t work in my case?

It was just a lucky coincidence that I tried the working solution.
But some bug in me won’t let me sleep well till I find a reason why.
I need my beauty sleep :-/
Your explanation will help me and many other nonsleeping wordpressers, I am sure … thank you, thank you, thank you ??