It shows OK in IE7 but not in IE6. Tested with Adobe Browser Lab.
From my experience, Adobe Browser Lab captures the client area only - it never includes the scroll bars on the window itself, even when they are present in the real browser.
I think that if you are seeing a scroll bar in Adobe Browser Lab then that is an additional scroll bar. A scroll bar that is in addition to any that might be on the window (the html element).
Come to think of it... IE6 and IE7 always have a vertical scroll bar present on the browser window (greyed out when not required)!? And this certainly seems to be the case in IE8 under "IE7 Browser Mode" and in IETester (IE6 and IE7). This probably explains why trying to set overflow-y:scroll on the body produces an additional scroll bar in these browsers!