It seems that the session ID remover have a small bug.
With the original configuration:
define('PHPDIG_SESSID_VAR','PHPSESSID,s');
every variable passed in the URL ending with one value of PHPDIG_SESSID_VAR are disregarded.
I add a problem with index.php?series=001 turned into index.php?serie.
Where is the function that uses PHPDIG_SESSID_VAR?