In looking at the facebook share code, you set $params to the post URL, but nothing else. While Facebook is good at page scraping, it will NOT put content in the "message" field.
I have resolved this by adding this code in includes/oauth/adapters/facebook/client.php:
$params['message'] = $data->content;
That simple! You set $data from a call to getting the post's info, in fact.
I'd have to have to add this back every time I update, and I don't believe this file can be overridden.
Is there any way you can set this? It's required in the graph API call to set a post's content properly.