Description:
------------
When the body of a POST request grows too large, PHP stops decoding 
the passed-in cookies properly. Usually this results in a session 
that is dropped (the user being logged out, etc.)

Reproduce code:
---------------
<?
  session_start();

  $FIELDS = 200;
  ?>

  PHP Version: <b><?= phpversion() ?></b><br>
  Cookies: <b><?  print_r($_COOKIE);l ?></b><br>
  Session ID: <b><?= session_id() ?></b><br>

  <form method="post">
  <input type="submit" value="Send">
  <? for ($i = 0; $i < $FIELDS; $i++): ?>
      <input type="text" name="field[$i]" value="<?= md5(microtime()) ?>">
  <? endfor ?>
  </form>



Expected result:
----------------
Session id does not change between posts, cookies are displayed.





Actual result:
--------------
Depending on the setting of $FIELDS, PHP does or does not drop the 
cookies and therefore the session.

On my setup, setting $FIELDS to 100 works fine and the session is 
maintained, setting $FIELDS to 200 exhibits the behaviour mentioned.