I believe that the problem was caused by the web server not being configured to load index.php when a directory is requested. Apparently when you run index.php, at some time it reloads itself via a directory request, and if the directory request doesn’t load index.php, all you get is a directory listing. I changed this on my web server, problem goes away. I installed wordpress into a different directory for my daughter, and same problem! Set that directory to default to index.php, problem goes away.
