Server is standard Linux server on Amazon Web Services. Cent OS 5/Apache/PHP 5.3. No APC.

It's worked fine for over a year, but now when I edit some but not all PHP files on the server using vi, the changes don't affect the web output.

For example, I edit myfile.php and put a die() at the top, but when I load the page in my web browser, instead of the die() I see the content that would show up if the die() weren't there. svn updating the file in question doesn't help either.

Files are on an Amazon EBS partition symlinked to /var/www/html. Just to reiterate -- this has worked fine for a long time.

Restarting apache didn't help, nor did rebooting the server. What's weird is that it's just some of the files but not all. File ownership/permissions are the same for the "good" and "problem" files.

I'm not a Linux newbie but am at a complete loss with this, and couldn't find anything on Google either. Any hints would be much appreciated!