It seems that the 'unset' function fails to handle empty array keys properly:

<?

$z = array();
unset($key);

echo "Test unset with key = '$key'<br>\n";

$z[$key] = 1;
unset($z[$key]);

while( list($k, $v) = each($z) ){
  echo "$k: $v <br>\n";
}

$z = array();
$key = 9;

echo "Test unset with key = '$key'<br>\n";

$z[$key] = 1;
unset($z[$key]);

while( list($k, $v) = each($z) ){
  echo "$k: $v <br>\n";
}

?>