I found the min-height in the feature image code was being set to the
original height of the image. I changed the min-height to 400px to
match the max-height.
if (has_post_thumbnail()) {
$image_data = wp_get_attachment_image_src(get_post_thumbnail_id(), "full");
echo '<header id="still" style="background: url('.$image_data[0].');'
- . 'min-height: '.$image_data[2].'px;max-height: 400px"></header>';
+ . 'min-height: 400px;max-height: 400px"></header>';
} else {
echo '<header id="still" style="background: url('.get_template_directory_uri().'/assets/default-header.jpg);'
. 'min-height: 400px;max-height: 400px"></header>';