Wordpress: Getting Month by Month posts, issue with layout - php

Question

I've got an issue where I'm getting the wordpress posts month by month, but I'm missing something obvious where by it screws with my layout a bit. I'm using the 996 grid system for my layout.
The NEED:
I'm getting all posts in March 2013 and wanting to lay them out each inside a so 3 posts are stacked like screenshot A.
My code is below:
<div class="container clearfix" style="background:yellow;">
<div class="grid_12" style="background:blue;">
<?php
$blogtime = date('Y');
$prev_limit_year = $blogtime - 1;
$prev_month = '';
$prev_year = '';
$args = array(
'posts_per_page' => 20,
'ignore_sticky_posts' => 1
);
$postsbymonth = new WP_Query($args);
while($postsbymonth->have_posts()) {
$postsbymonth->the_post();
if(get_the_time('F') != $prev_month || get_the_time('Y') != $prev_year && get_the_time('Y') == $prev_limit_year) {
echo "<h2>".get_the_time('F, Y')."</h2>\n\n";
}
?>
</div>
<div class="grid_4" style="background:red;">
<article id="post-<?php the_ID(); ?>" role="article" itemscope itemtype="http://schema.org/BlogPosting">
<?php the_post_thumbnail('standard-thumb'); ?>
<h3><?php the_title(); ?></h3>
</article>
</div>
<?php
$prev_month = get_the_time('F');
$prev_year = get_the_time('Y');
}
?>
</div> <!-- END OF CONTAINER -->
THE PROBLEM:
With the above code, every single instance of grid_4 sits outside the container EXCEPT the first one. See Screenshot B
How can I make sure all grid_4 divs are included inside the container?
I've tried moving the div which doesent work, I think I'm missing something fundamental from the query.

Answer 1

So it seems if I remove the closing div to grid_4 - it now works...
In the dom it now all sits inside the container... however looking at the template markup code I'm one div short...
I don't know why this is happening but it is... one day I'll figure out why but right now wordpress is automagically adding an extra div.