Honestly i'm not sure what the issue is because i'm not familiar with the theme, but the initial suggestion was simply something that stood out as being odd when i looked at the source of the page.
You could try removing the non-essential code, like post markup, and see if the layout fixes itself, if it does, then there's something in the code that was removed causing the issue, if not, then the issue lies with the theme's markup.
You could also run your page through the validator to, it should help spot any invalid/problem code like missing closing/opening tags and such.
http://validator.w3.org/