Put a variable SESSION in an other variable, delete SESSION content variable - php

Question

I've an application in PHP 4.3.9 and I've a problem with SESSION.
When I put a variable SESSION in an other variable, like this :
$tempInsInscription = $_SESSION['ins_inscription'];
$_SESSION['ins_inscription'] content is removed.
I don't understand why. Is a PHP4 particularity ?
EDIT
I tried many case to found where exactly I lose my content and this is in a foreach :
reset($tempInsInscription);
foreach($tempInsInscription as $key => $ins_inscription){
if(is_array($ins_inscription)){
reset($ins_inscription);
foreach($ins_inscription as $key_etape => $etape){
$_SESSION["dossier"][$key_etape]=$etape;
}
}else{
$_SESSION["dossier"][$key]=$ins_inscription;
}
}
SOLUTION
I found a solution to solve my problem. here my new code & it's works perfectly :
$tempInsInscription = $_SESSION['ins_inscription'];
$_SESSION['ins_inscription'] = $tempInsInscription;
reset($tempInsInscription);
while(list($key, $ins_inscription) = each($tempInsInscription)) {
if(is_array($ins_inscription)){
reset($ins_inscription);
while(list($key_etape, $value_etape) = each($ins_inscription)) {
$dossier[$key_etape]=$value_etape;
}
}else{
$dossier[$key]=$ins_inscription;
}
}

Answer 1

SOLUTION
I found a solution to solve my problem. here my new code & it's works perfectly :
$tempInsInscription = $_SESSION['ins_inscription'];
$_SESSION['ins_inscription'] = $tempInsInscription;
reset($tempInsInscription);
while(list($key, $ins_inscription) = each($tempInsInscription)) {
if(is_array($ins_inscription)){
reset($ins_inscription);
while(list($key_etape, $value_etape) = each($ins_inscription)) {
$dossier[$key_etape]=$value_etape;
}
}else{
$dossier[$key]=$ins_inscription;
}
}