strange i.e. vs. non-i.e. XMLHttpRequest.requestXML response

I have made sure that the code to get the XML (above what is shows
*DOES WORK* for all browsers).... but when I do the following line IE
reports "Object" and everything else "XMLDocument"... the problem this
causes will be explained below:

if(reply.substring(0,"<?xml".length)=="<?xml")
return sRequest.responseXML;

this is a problem in that the following line (that calls the above
code) reports "0" to IE and "1" when processing exactly the same XML:

<?xml version="1.0" ?>
<ISUReply>
false
</ISUReply>

Here is where I get differing results:

alert(callRCI("isLoggedIn",[]).getElementsByTagName
("ISUReply").length);

Specifically:

ff/safari/opera: 1
ie7/8: 0