This is something I've noticed on occasions when using IIS on Windows. However, the files are created in a temporary folder that gets automatically cleaned periodically, so I don't worry about it. However, it has crossed my mind to figure out was causing it, but seeing as it seemed to happened only when using IIS, I'd just assumed that M$ had not implemented a clean up. If you're using another web server/OS, I'd be interested to know.
Barbie | Birmingham Perl Mongers | http://birmingham.pm.org/