Possible bug with set-cookie

Hi,

I have this script:

<?php setcookie('testcookie',str_repeat('a',$_REQUEST['l']), (time()+(86400*30))); ?>

If I execute it, with:

http://$url/test.php?l=1799

it works.

If I switch from 1799 to 1800, nginx stop serving this page.

It appens only with nginx. Apache is works good maybe by deleting cookie
or
simple overwriting another.

How can solve this?

Bye.