cookie值取决于在URI中包含'index.php'

I have got simple 'index.php' for detecting cookie values:

var_dump($_SERVER['SCRIPT_NAME']);
var_dump($_COOKIE);

When I invoke it form the browser like that http://dev.isos.org.pl/index.php I get the following answer:

string(10) "/index.php"
array(2) {
  ["ISOSid"]=>
  string(32) "ba130ff42c56a22b85adc5952e0f0fbb"
  ["ISOSnonce"]=>
  string(8) "11193333"
}

When I invoke it without 'index.php': http://dev.isos.org.pl I get different cookie values:

string(10) "/index.php"
array(2) {
  ["ISOSid"]=>
  string(32) "4d3d82fc3c99c301663ee3831986ffa8"
  ["ISOSnonce"]=>
  string(8) "53268338"
}

Such behaviour is unexpected and not desired. How to correct it - to get the same values each time?