EDIT: Well in reviewing the zoom functionality further - it seems there is more here than meets the eye. Is there a way to do an absolute zoom? As some of my mockups use more canvas than others.
Well the first problem is that I do not use command-zero as my default zoom, I use command-zero and then command-plus (basically zoom one level).
But setting that aside, one of the issues is that the focus seems to remain on the last selected item for a markup. So if there is an item selected, and I leave the markup, then return, that item is still selected. Then any zooming will be relative to that item rather than just defaulting back to the upper left part of the canvas.
So it seems to me that one thing that could help is an option that deselects all objects in a mockup when another mockup in a project is edited. I realize that there is probably an interest for having that strictly as an option. as I see the need to have the zoom and focus remain for mockups, especially complex ones. But my mockups are all the same size by design so I can move quickly between them.
I use Keyboard Maestro - maybe I can mock up something that will force the behavior.
Anyway, am still looking at the various interactions and will try to report back anything insightful.