Unsetting References
When you unset the reference, you just break the binding between
variable name and variable content. This does not mean that
variable content will be destroyed. For example:

<?php
$a = 1;
$b =& $a;
unset ($a);
?>
won't unset
$b, just
$a.
Again, it might be useful to think about this as analogous to Unixunlink call.