What's Wrong With: Var T = New Array(-1);

if I put the line:

var T = new Array(-1);

anywhere in my script, it stops working. e.g

<SCRIPT LANGUAGE="JAVASCRIPT">
<!--
var T = new Array(-1);
document.open();
document.write('hahahah');
-->
</SCRIPT>

doesn't produce any output. If I change

var T = new Array(-1);

into

var T = new Array(1);

or

var T = new Array(-1,-1);

everything works fine again.
Same results in Mozilla 1.7.2 as in IE 6.

Is that a bug in both their javascript interpreters or can anybody
give me a good explanation of why that is?