On my blog WordPress returns an empty post with today's date if I do a search for one letter, e.g. ?s=a or ?s=q Is this a known bug, and how do I fix it?
Searching using just one letter isn't really a good thing to do. Result wise, many posts should match the search query. On my site and testbed it does return results, I don't think they are particularly valid, but there are results. So it sounds like something is up with your install, but unless it is causing other issues, I wouldn't really worry about it.