Empty Post__in WordPress problem

Ran into a funny thing today. If you're performing a wordpress search with WP_Query, and you're using the post__in parameter to specify an array of ID's to retrieve and your array is empty then you end up with the post__in field ignore entirely and the other parameters taking precedence.

This is rather strange, as I'd expect it to show 0 posts since no ID's would match an empty list.

Specifically, my arguments to WP_Query were along these lines:

    $query_args = array( 	 
    'post_type' => 'redacted',
    'post_status' => 'publish',
    'posts_per_page' => $limit,
    'paged' => $page,
    'post__in' => $ids,
    'meta_key' => '_expiration_date', 
    'meta_value' => time(), 
    'meta_compare' => '>=',
    'ignore_sticky_posts'= > true
    );

If my ids array was empty, then I'd just get everything back. Which isn't what I wanted at all, so to fix the problem I just initialized the array with -1 and it all worked the way I expected it to.

Well, weirder things have happend. I wonder if this is a WordPress bug or intentional?