Sidebar Formatting Errors on Single Post Page

I recently completed a new WP installation and have yet to make any manual changes to the theme I am using. However, when viewing a single post page, the text in the sidebars becomes centered, and a graphical element from the main column (which is normally behind the sidebars) floats in front of the sidebars. I can’t figure out why, especially as I have yet to directly edit the theme. (Although I have installed several widgets and plugins.)

Any suggestions on how to tackle this? Thanks!

Problem page:
http://www.ftm.koumbit.org/robmaguire/blog/archives/1

Home page:
http://www.ftm.koumbit.org/robmaguire/blog/

Theme demo (how single post should look!):
http://demo.jauhari.net/?p=3