Well, circling text when you have a highlight feature available would be pretty silly, so I don't think getting the zoom to preserve that should be a priority. What should be preserved are the size of markings in a margin or in other whitespace. ie, when you write a note in the right margin while zoomed in, it should shrink with the rest of the text (and stay in the margin) when you zoom back out, rather than staying the same size and now covering up part of the text.