This is a quirky issue with Expression Web. I see it all the time. What I do is open the site in FrontPage 2003 and work on my editing if I need to, then change only the CSS styles in Expression web. There really isn't a "fix" for this.....unless we contact Microsoft and have them fix the issue. It has to do with the way the site is looking at the DIV layers and CSS. Use FP to edit. See if that helps.
-Joey