It was changed because for the most common use cases, the user wants to keep frame 0 visible. The old behavior resulted in frame 0 being pushed off screen for any amount of zooming in, so you'd then need to scroll or right click drag to get frame 0 back. Note we still do the old behavior if frame zero has been scrolled off screen.
I think we can improve it further by doing as we do now, but allow frame 0 to go off screen if required to keep the current frame on screen.
