custom php pages are redirecting to /

I just recently upgraded a Zen Cart website to 1.5.4.

I've created some custom php pages that work with Zen Cart and I usually test and debug through php pages from the root. For example, if I am having a session issue, I might make a file called session.php' which I request with example.com/session.php'.

In these files I usually just load 'includes/application_top.php' to have zen cart load everything it would normally load so I can test properly.

I keep running into a situation where making a request that isn't 'index.php' causes me to get redirected to '/' if I have loaded 'application_top.php'. I am assuming is it a security feature built into the new version of Zen Cart. I know it isn't an htaccess error because the file is requested fine without application_top and I have disabled htaccess as well.

Where is the check for this so I can turn it off and resume testing?