Weird mySQL problem with mod_rewrite

Hi, I'm encountering a very strange problem that's manifesting itself in mySQL. Basically, when accessing a PHP script using mod_rewrite URLs, e.g.: instead of http://www.domain.com/index.php?this=that using http://www.domain.com/index.php/that if that script accesses mySQL, mySQL is becoming flooded with "unauthenticated users" and after a couple of reloads it bogs the server down. If I access it in the normal GET way (the script can handle either URL method) this doesn't happen - we see no "unauthenticed users" in mySQL. Nothing else seems to be affected, only mySQL. I'm stumped as to what it could be. This isn't just happening on one server, it's happening on many. Does anybody have any ideas? Regards, G