[Plugin: WordPress SEO by Yoast] Site title duplicates on Facebook share?

When a user shares a post on Facebook (either using the Digg Digg plugin or the Social feature within WordPress itself) it reads the link as:
“<Post Title> – <Site Name> | <Site Name>”

What could be causing this? I’ve checked the WP Settings and the settings within the plugin itself but can’t identify anything that even relates to how Facebook reads the title, let alone anything that doubles up the %%sitename%%

Where should I be looking to rectify this issue?

I’m using the latest version of the plugin on the “Balance Theme” on the Genesis Framework (both by StudioPress).