get posts meta query returning the latest post if no meta key found

Posted: - Source : stackoverflow

I have this pretty standard script that looks for a preview or a report (custom post types) which have data stored against them (serialized array) taking the form of a guid.

The guid is present on my report and not present on my preview (this is intended as I want to catch the failure).

However, when I run the script for preview, the get_posts returns one post which seems to be the latest post published.

$args = array(
    "post_type" => array($type),
    "posts_per_page" => 1,
    "post_status" => "publish",
    "orderby" => "date",
    "order" => "DESC",
    "meta_query" => array(
        "key" => "_fixtures",
        "value" => $fixguid, // IN THIS CASE IT SHOULD BE 12AB1324
        "compare" => "="
    )
);  
$posts = get_posts($args);
return $posts;

The report (which has the meta data 12AB1324) is returned successfully but the preview returns the latest story which happens to have a value of 12AB3136.

I suppose my question is:

Why does get_posts meta query return
a) the latest post and
b) a post with a guid that doesn't = the given key parameter
.

Thanks.