What would cause PHP variables to be rewritten by the server?

I was given a VM at my company to install web software on. But I came across a rather bizarre issue where PHP variables would be overwritten (rewritten) by the server if they matched a specific pattern. What could rewrite PHP variables like this?

How to show Ajax requests in URL?

What I want is to have links which change a part of the page , and a dynamic URL for it, where I can specify variables such like #calendar=10_2010tabview=tab2

.htaccess subdomain argument not accessible in query string

I have written the following rules in .htaccess

RewriteCond %{HTTP_HOST} ^([^\.]+)\.domain\.com 

RewriteCond %1 !^www$ [NC]

RewriteCond %{REQUEST_URI} ^/news/news-details\.php$

RewriteRule (.*) news.php?div=%1

.htaccess mod_rewrite - how to exclude directory from rewrite rule

I have 8 lines of rewrite rules in my .htaccess file. I need to exclude two physical directories on my server from these rules, so they can become accessible. For now all requests are sent to index.php file.

redirect 404 to similar urls

I have a website with stories in it. I can have multiple types of stories within multiple categories like: