Most of the text on the center column is place below the text columns on the left and right side, when my Webkit window is maximized (1024x768). Reducing the window size a bit gives an almost correct layout. "Ads by Google" is inside the first codebox. Reducing the windows even more overlays the codeboxes on the right column. (this might by bad html coding).
Created attachment 15843 [details] Reduction Only happens in strict mode and with clipped overflow.
See FIXME at the bottom of RenderBlock::getClearDelta().
Safari, Chrome, and Firefox all agree on rendering for this test case. I don't believe there is any remaining compatibility issue.