Bug or hack? $GLOBALS

$GLOBALS["items"] = array('one', 'two', 'three', 'four', 'five' ,'six', 'seven');
$alter = &$GLOBALS["items"]; // Comment this line
foreach($GLOBALS["items"] as $item) {
  echo get_item_id();
}

function get_item_id(){
  var_dump(key($GLOBALS["items"]));
}

Check output of this code, with commented and uncommented second line. My result(PHP 5.3.0). With second line

int(1) int(2) int(3) int(4) int(5) int(6) NULL

Without second line:

int(1) int(1) int(1) int(1) int(1) int(1) int(1)

Why so strange result?