User blog comment:Sarah Manley/Updates to the Editor Redesign/@comment-477304-20110707224225/@comment-126761-20110712144454

Okay, so it exists to prevent the line under section titles hitting the thumbnail. Since you have a transparent background, it means it means the colour matching doesn't work. A suggestion is this CSS: which is a bit closer your article background. If you're okay with the lines touching, you could put transparent instead of #F6F6F6.