User blog comment:Rappy 4187/Technical Update: October 2, 2012/@comment-3187795-20121004224818

Issue I found with the new layout: The Theme Designer preview is not updated to match the current width.

When you begin, everything is fine and the content area width is normal. When you upload a new file, the window shrinks back to how it was pre-update. That leads to making updated backgrounds skinnier than they should be to accominate the phantom dimentions. This issue harassed me all last night.