I have two fairly similar blogs running Comet 1.2.5 by Frostpress. Their sidebars are very similar as well. But one of them has started putting the sidebar at the bottom of the page, the other is fine. On the one that is causing a problem the sidebar goes back to its rightful place if you go to the individual post page and the 'About' page is functioning fine. I don't think I've done anything different to the blog recently.
The 'bad' sidebar is at http://www.oneforthecrow.com/painting
The 'good' sidebar is at http://www.oneforthecrow.com/studio