The elements in columns are so because they're in a different HTML structure and have CSS applied to them.
Each correctly positioned column has this HTML structure:
<div id="cms-column">
<article id="post-5243" class="post-5243 post type-post status-publish format-standard hentry category-damesmode category-tunieken">
<header class="entry-header">
<div class="comments-link">
</div>
</header><!-- .entry-header -->
<div class="entry-content">
<div style="background-color:#F2F2F2; width: 170px; height: 300px;float: left;">
<center>
<a href="http://www.kledingfreak.nl/damesmode/D39ccb2398b3ca8778b9b10e12cbf793f/"><img src="http://www.fashionfactor.nl/images/P/IMG_0247.jpg" style="max-height: 160px; max-width: 160px"></a><br>
<strong>ALYNA</strong><br>
<span style="white-space: nowrap;">Jersey Poncho</span><br>
<a href="http://ds1.nl/c/?wi=173273&si=2686&li=1114132&dl=product.php%3Fproductid%3D16437&ws=">Nu kopen</a><br>
€49.95<br>
<a href="http://www.kledingfreak.nl/damesmode/D39ccb2398b3ca8778b9b10e12cbf793f/">Details</a>
</center></div>
</div><!-- .entry-content -->
<footer class="entry-meta">
</footer><!-- #entry-meta -->
</article><!-- #post-5243 -->
</div>
Each incorrectly positioned column has this HTML structure
<article id="post-5237" class="post-5237 post type-post status-publish format-standard hentry category-damesmode category-jurken category-jurken-jurken">
<header class="entry-header">
<div class="comments-link">
</div>
</header><!-- .entry-header -->
<div class="entry-content">
<div style="background-color:#F2F2F2; width: 170px; height: 300px;float: left;" id="cms-column">
<center>
<a href="http://www.kledingfreak.nl/damesmode/Da20fe51d23de4175c9ded8d91ab2ae67/"><img src="http://www.fashionfactor.nl/images/W/IMG_7278.jpg" style="max-height: 160px; max-width: 160px"></a><br>
<strong>ALYNA</strong><br>
<span style="white-space: nowrap;">Dress to Kill </span><br>
<a href="http://ds1.nl/c/?wi=173273&si=2686&li=1114132&dl=product.php%3Fproductid%3D16431&ws=">Nu kopen</a><br>
€89.95<br>
<a href="http://www.kledingfreak.nl/damesmode/Da20fe51d23de4175c9ded8d91ab2ae67/">Details</a>
</center></div>
</div><!-- .entry-content -->
<footer class="entry-meta">
</footer><!-- #entry-meta -->
</article>
So it just looks like you're missing a containing HTML element <div id="cms-column"> that should wrap around each item.