Zooming OUT should re-execute the search since you are now including new content (when zooming OUT you are including more time than the original search). Whether or not re-execution happens during zoom IN is a different matter (and doesn't appear to be your question).
UPDATE: If we look at the Jobs page (Activity > Jobs), we can see that zooming in and out all create new jobs that run. Doesn't that answer our question? In my case I can see jobs running for both zoom in and out.