Vanilla 2

I have noticed that in some browsers, while the prettyphoto is open, you can still scroll the main window (which is in the background), this creates a flickering in the overlay.

I have read that some people have disabled the auto-centering in the window, so the overlay moves with the scrollbars, but is there a better solution? Why is the centering so choppy? Would it be possible to limit the scrolling to the overlay size? That way, unless the the overlay is larger than the viewport, no scrolling is possible, and when the overlay is larger than the viewport, the scrolling is limited to the overlay?

Thanks