Description:
------------
session_regenerate_id() destroy the false constant : it destroy the constant sid in lower case instead of the constant in upper case...

In PHP sources :
/* if the SID constant exists, destroy it. */  zend_hash_del(EG(zend_constants), "sid", sizeof("sid"));

should maybe be

/* if the SID constant exists, destroy it. */  zend_hash_del(EG(zend_constants), "SID", sizeof("SID"));

(file session.c)

(Please excuse me for my bad english ;-))

Reproduce code:
---------------
<?php
define('sid', 'essai');

session_start();
session_regenerate_id();

echo SID."\n";
echo sid;
?>

Expected result:
----------------
jg9vejq8p3e15lfu34vbouc6j3
essai

Actual result:
--------------
Notice: Constant SID already defined in D:\essai.php on line 5

Notice: Use of undefined constant sid - assumed 'sid' in D:\essai.php on line 8
sid