wp shortcode breaks get_post_thumbnail - shortcode

Question

I'm having some trouble with short code's breaking a featured image I have set on my home page in Wordpress (4.0). For some reason, when I paste in my shortcode in the wp-admin > page > edit > content for the home page, suddenly my featured image stops working. It's working until I paste in the shortcode and update the page, but then the image disappears and the_post_thumbnail() returns false. I've also tried get_the_post_thumbnail() without success.
Here's my code excerpt from "front-page.php":
<div class="small-12 medium-6 columns">
<?php while ( have_posts() ) : the_post(); ?>
<h1><?php the_title(); ?></h1>
<?php the_content(); ?>
<?php endwhile; ?>
</div>
<div class="small-12 medium-6 columns">
<?php if (has_post_thumbnail()) {the_post_thumbnail();} ?>
</div>
And here's the shortcode function from "functions.php":
// [random_testimonial]
function short_code_get_random_testimonial(){
$args = array( 'post_type' => 'testimonial', 'posts_per_page' => 1, 'orderby' => 'rand' );
$query = new WP_Query( $args );
while ( $query->have_posts() ) : $query->the_post();
$random_testimonial = get_the_content();
$author = get_the_title();
$rt = '<p class="quote">' . $random_testimonial;
$rt .= '</p><p class="right">– ' . $author . '</p>';
endwhile;
return $rt;
}
// Register the shortcodes.
add_shortcode( 'random_testimonial', 'short_code_get_random_testimonial' );
// Allow text widgets to contain shortcodes.
add_filter('widget_text', 'do_shortcode');
add_filter('the_content', 'do_shortcode');
Any ideas would be greatly appreciated.

Answer 1

I think I may have solved this one. It seems to have something to do with the fact that I was calling a custom post type with the shortcode, so by the time the_post_thumbnail() was called, the query had changed to refer to the custom post type included in the shortcode ("testimonial") rather than the parent post (in this case the home page). I revised my code as follows to catch the image before the shortcode is called, and all is working again:
<div class="small-12 medium-6 columns">
<?php while ( have_posts() ) : the_post(); ?>
<?php
// go ahead and get the post image in case [random_testimonial]
// shortcode is used in page content which will break the query.
if (has_post_thumbnail()) {$image = get_the_post_thumbnail();} ?>
<h1><?php the_title(); ?></h1>
<?php the_content(); ?>
<?php endwhile; ?>
</div>
<div class="small-12 medium-6 columns">
<?php
// Echo post image from above.
if(isset($image)){echo $image;}
?>
</div>