jQuery UI对话框:IE 8后台的一个大DIV

I'm trying to use jQuery UI's modal dialog and testing my stuff in IE8. Every time dialog pops up, a huge DIV is being created on the background and IE keeps changing vertical scroll bar's thumb size and if there was a huge page downloading in the background. In compatibility mode IE changes vertical scroll bar's thumb once, everything works as expected and it doesn't look like the page is still loading. jQuery UI's sample works for me just fine.I'm trying to use jQuery UI's modal dialog and