New image size not showing correctly

I am creating a child-theme based on 2013.

I am trying to add a new image size and have it selectable in the media modal.

I have checked that a new, correct sized image is being created ie 670px wide

But the modal window is showing it as being 604px wide and when inserted you get:

<img width=”604″ height=”453″ alt=”two-new-honeys” src=”…/two-new-honeys-670×503.jpg” class=”..”>

Its putting in the right image, but adding in wrong width and height values in the html

What can I do to get the right width / height

In functions.php I have added:

// add new image size(s)
add_theme_support( 'post-thumbnails' );

add_action( 'after_setup_theme', 'bsb_add_image_size' );
function bsb_add_image_size() {
  add_image_size( '2-column', 670 ); // 670 pixels wide (and unlimited height)
}

add_filter( 'image_size_names_choose', 'my_custom_sizes' );
function my_custom_sizes( $sizes ) {
    return array_merge( $sizes, array(
        '2-column' => __( '2 Column width' ),
    ) );
}