WordPress 4.0 and the video shortcode

I had the same issue. I solved it be adding a float to the video class in my dashboard. This was done by adding a CSS snippet to my theme’s functions file:

//Add CSS to Dashboard (fix for WP-Help)
add_action('admin_head', 'wphelp_fix');

function wphelp_fix() {
  echo '<style>
		#cws-wp-help-document .wp-video { float:left;}
  </style>';
}