I've recently updated to last version of the plugin (4.1.6) and since then I see that when I have a youtube in my post's content, the plugin auto inserts to the head section the meta property for facebook - og:image
This is a bad behaviour, since in most cases posts will have another og:image already in page, with the appropriate image for facebook.
So this plugin makes that meta duplicates and facebook sometimes chooses to prefer the og:image of the plugin and sometime og:image that is there with the real featured image.
The code locate in smartyoutube.php, lines 136-148
if ( isset( $matches ) ) if ( $matches != '' ) echo '<meta property="og:image" content="http://i.ytimg.com/vi/' . $matches . '/default.jpg" />';
It will be best if plugin's developer will add an option to set this on/off, or to filter this out.
Right now the only way to change this is change in plugin's source code, which will be erases upon next update.