This caught me out:

        unset($tarray);
        unset($undefined);
        $tarray["one"] = 1;
        $undefined =& $tarray["two"];
        while (list($key, $value) = each($tarray)) {
                echo $key . "|" . $value . "<br>";  
        }

That code will generate this output:

one|1
two|

So you can see that the 4th line of the code creates a key "two" in the
array with an unset value.

I don't think it should do that.  After all, this code:

	unset($undefined);
	unset($not_there);
	$undefined =& $not_there;

generates precisely nothing.