This feature is also available in build 7229. If you notice when you hover over the preview boxes, one of them will be highlighted. This is the currently selected tab. If you scroll up and down on this, both the preview and the full screen will scroll. Moving to another preview box, the full image of that will appear on screen. However, when scrolling the original preview and screen (which you can no longer see) will scroll because that is still the active party. To make another preview the active one, you need to click on it (or select the appropriate tab in the main window).