If you have the Split Preview open with the page position at halfway (vertically), you then make a change in the code and save it, the Split Preview pane not only updates itself automatically but it also remembers its halfway page position and stays there.
That's convenient in itself. But why does full Preview pane not do the same (it jumps back to the top of the page)? Can you please make it stay where it was? Most websites need a proper full Preview to see the effect of changes, most certainly if one is working on the lay-out.