This is a strange one.
My ISP runs Apache 1.3.27 and offers PHP 4.3.6. (I can confirm the Apache version, but not the PHP version, so I'm taking their word for it.) We are running into a strange problem that we both are having trouble diagnosing.
Put simply, when I browse to a *.php URI, the PHP processor doesn't process the file (or isn't invoked), but when one of the ISP support staff browses there, the PHP processor does process the file.
We're going to the same URLs, from different IP addresses (naturally) and getting different results. In one case, the PHP processing occurs, and in the other, it doesn't.
Any general ideas where the problem might lie?