Left sidebar not on left if custom logo uploaded and no user sections

(Perhaps this depends on the size of the custom logo; I'm not sure.)

After uploading a custom logo on a site with all regions empty of blocks except the left sidebar, the left sidebar is positioned in the horizontal middle of the page (instead of on the left), with the main content below it and flush left.

For my purposes this was solved by adding style="clear:both" in the id="middlecontainer" div tag. The attached patch does that.