This is a strange issue. I am using the Publicize module to link to a Twitter account, but not a Facebook account. When the URL of a published post is copied from the browser's address bar and pasted into a Facebook status box, the URL it reads is the Twitter-ized one. Facebook then doesn't pull any of the content or images in.
When I go into the post's header and copy/paste the WordPress-generated short URL it works just fine.