Strange Bizzare Problem

I'm running into this really odd, seemingly illogical problem: Background: This is an on-line course made up of lots of pages, some have forms, some don't. The pages which have forms all submit to single php script (called submit.php) which processes the submitted form, placing the submitted answers into a database and updating a variable which tracks which pages of the course have been completed by the user. The submit.php page, once it has processed the submitted form data, then does a http redirect so the student is served the next page of the course. Problem: About 1 out of 20 times submit.php doesn't update the database, or update the variables tracking student progress, but does the http redirect. submit.php looks something like this: if ($fsubmit){ update database; update variable; http redirect to next page; } Conclusion: Is it possible that PHP can skip php instructions before an http redirect semi-randomly? The same problem occurs with output buffering on or off. Any theories on what the problem may be? Thanks, Andy.