While fixing some .htaccess/redirection issues to get LiveJournal to point to a recent RSS feed, I was using an old Java program I wrote to see the headers/guff Apache was giving me:

HTTPimp gives me a 404

After trying the preview button that shows the request headers HTTPimp sends, I identified a bug - when it breaks the URL into address, path, and query parts, it mostly stitches them together correctly, except for the ? between path and query.