Why is this a problem?
<?php
$array = array(1);
$array[] = &$array;
?>
This is why:
/Zend/zend_hash.c(416) : Freeing 0x08434674 (35 bytes), script=circular.php
/Zend/zend_execute.c(2015) : Freeing 0x08434614 (44 bytes), script=circular.php
/Zend/zend_API.c(562) : Actual location (location was relayed)
/Zend/zend_hash.c(188) : Freeing 0x0843E414 (32 bytes), script=circular.php
/Zend/zend_execute.c(2035) : Freeing 0x0843DCB4 (12 bytes), script=circular.php
/Zend/zend_execute.c(499) : Freeing 0x0843DC74 (12 bytes), script=circular.php