Problem with OpenGraph Protocol

I’m having some trouble with what shows up when I attempt to share posts on Facebook.

Some of my posts will include an image, a nice description and title. Others don’t.

I’m not doing anything different on the publishing end of things. Each post has an image. They are of the same post type, using the same theme and template files.

But I get very different results when trying to share them on Facebook.

Any idea what’s going on? Here’s a sample post that’s having problems.
http://virginiahumanities.org/2012/11/master-of-the-mountain/

And here’s one that behaves as expected:
http://virginiahumanities.org/2012/11/picturing-antietam/

Thanks!

http://wordpress.org/extend/plugins/simple-facebook-connect/