has_post_thumbnail always returns true in 3.6

The problem is quite easy. has_post_thumbnail always returns true.

<article class="box-<?php echo $counter--; ?>">
		<h2 class="entry-title"><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
        <?php if ( has_post_thumbnail() ) : ?>
			<a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_post_thumbnail(); ?></a>

		 <?php else : ?>
			<a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>">TESTING</a>
		<?php endif; ?>
		</article>

This will always return the first snippet and never the else-function, even when there is no featured image there. (Yes, this is put in the loop.)

– No plugins
– Making a child theme of “2013”