When you open the Start menu and type into the search box, sometimes the first search result is autoselected (so you just have to hit Enter), whereas sometimes See more results is autoselected. Is there a method to this madness?

If an item is found in the Programs and Control Panel sections, then the first such is autoselected. Otherwise, the default item is See more results. The theory is that if you are typing a program or control panel name from muscle memory and make a typo, you don’t want this to result in a random file opening. (Why are programs and control panels treated differently? Because the list of programs and control panels is relatively static, permitting the development of muscle memory. On the other hand, the other sections like Files and Communications are highly dynamic, and it’s unlikely that you’re going to get in the habit of always seeing Budget Proposal as the first hit because in an hour’s time, it might not be.)