[4.0.1] Buffered Grid vertical scrollbar click not working on IE9 but work on Chrome.

The behavior in Chrome is when you click in the middle of the scrollbar between the cursor and the arrow, the cursor will move of one page in direction of the click.

Also keyboard doesn't work in any browser, so far from meeting any minimum "Accessibility" standard.

http://dev.sencha.com/deploy/ext-4.0...ffer-grid.html