Demonstrate block regions not displaying correctly

First let me say what a great theme. I'm thoroughly enjoying it.

I've come across a minor issue when on the blocks administration page. I'll select the 'Demonstrate block regions' link to see where regions appear on the page. The two sidebars are displayed below the content bottom (see attached). This appears to only happen on this preview and not when actually presenting content.

Not sure if this relates to #814730: The layout will break on some admin pages if there are two sidebars enabled at all.