Mod Assign view parameters - useridlistid

The file that process mod/assign/view.php

can handle a parameter useridlistid that helps to identify the array in the cache system... well in theory:

I was wondering 

why does this parameter reads form 'action' instead of 'useridlistid' as it should?

$urlparams = array('id' => $id,
'action' => optional_param('action', '', PARAM_TEXT),
'rownum' => optional_param('rownum', 0, PARAM_INT),
'useridlistid' => optional_param('action', 0, PARAM_INT));

Thanks