date_query not returning some posts but they seem to be in correct date range

I'm getting some very strange results with the date_query parameter of get_posts. I have a post for which:

date('Y-m-d H:i', get_post_time('U', false, $postid))

returns:

2014-04-03 10:42

This post is returned fine from get_posts with these arguments:

$args = array(
    'post_type' => 'post',
    'cat' => 41,
    'fields' => 'ids'
);

But not with these:

$args = array(
    'post_type' => 'post',
    'date_query' => array(
        'after' => '1980-01-01',
        'before' => '2100-01-01',
    ),
    'cat' => 41,
    'fields' => 'ids',
);

Other posts seem to come back fine. What could be up? Does date_query query something different to get_post_time?