That does sound suspicious. I just checked on our test WP instance, and it all works fine. Both with the URL on a separate line and as the shortcode.
Let’s try to find what the problem is.
– What’s your WP version?
– If you see an empty post now rather than FB link, it is likely that the code shows up but wouldn’t work on your page. Can you check the view-source: of a post to see if the embed code is there?
– And if it is in the source code, but wouldn’t show up – can you open the JavaScript console and see if there are any scripting errors in it?
Both page’s source and JavaScript console are called from View->Dev Tools (or similar) or by right clicking on the page.
Thanks