Option "Stretch the sidebars and the content area down to the footer" option is enabled. However sidebar is not stretched:
Upgrade Parallels Web Presence Builder to the latest version and republish the site. Use the following command to upgrade Parallels Web Presence Builder component of Parallels Plesk:
~# /usr/local/psa/admin/bin/autoinstaller --select-release-current --install-component base --reinstall-patch
Re-publish the site.