$_SERVER['REQUEST_URI'] doesn't match url - php

Question

I uploaded a new website in a sub-folder of my server documentroot (www.example.com/demos/website-name) as I've always done to show demos to my clients.
In my cms I use mod_rewrite to push all requests to index.php and an "internal" rewrite in php, so I have to retrieve the $_SERVER['REQUEST_URI'] to read it and load the correct page.
Quite randomly (and only when the cms is placed in a subfolder like this case) the REQUEST_URI doesn't match the uri in the browser but remains the previous one: for example I'm in "/cms/foo", i click a link that brings me to "/cms/bar", the page reloads but if i dump the REQUEST_URI I still get "/cms/foo".
I really can't understand how this is possible.
This is how the .htaccess looks like:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ index.php [QSA,L]
And here it is how I retrieve the REQUEST_URI (MainConfig::ROOT_URL is the sub-folder path "/demos/website-name"):
public static function getPath()
{
if(isset(self::$cache['path'])) {
return self::$cache['path'];
}
if(isset($_SERVER['REQUEST_URI'])) {
$path = str_replace(MainConfig::ROOT_URL, '', $_SERVER["REQUEST_URI"]);
$path = explode('/', $path);
if(trim($path[1]) == '') {
$path = array();
}
unset($path[0]);
$path = array_values($path);
for($i = 0; $i < count($path); $i++) {
$fragment = $path[$i];
if(strpos($fragment, '?') !== false) {
$lastPathIndex = $i;
break;
} elseif(strpos($fragment, 'index.php') !== false) {
$lastPathIndex = $i;
break;
}
}
if(isset($lastPathIndex)) {
$lastPathElement = array();
$length = count($path);
for($i = $lastPathIndex; $i < $length; $i++) {
$lastPathElement[] = $path[$i];
unset($path[$i]);
}
$lastPathElement = str_replace('index.php', '', implode('/', $lastPathElement));
}
if(isset($lastPathElement)) {
$path[] = $lastPathElement;
}
} else {
$path = array();
}
$path = array_values($path);
self::$cache['path'] = $path;
return $path;
}