cloneNode in a xpcom component failed

Hi,

Context : 1.9.1 recent build, windows

// In a JS component, I load a DOM (from chrome://)
var vXhrComp = Components.classes["@mozilla.org/xmlextras/
xmlhttprequest;1"];
var vReq = vXhrComp.createInstance
(Components.interfaces.nsIXMLHttpRequest);
vReq.open("GET", "chrome://mychrome/content/myFile.xml", false);
vReq.send(null);
var vXml = vReq.responseXML;

//I want to "backup" my dom
var vXmlBackup = vXml.cloneNode(true);

The cloneNode failed : Security Error: Content at moz-nullprincipal:
{c0db3ee1-d7c3-47e4-b6d9-0a08830f15c9} may not load or link to //
chrome://mychrome/content/myFile.xml.

I think it's a problem with transfering nsIPrincipal to the new
Document.

In a xul page in chrome, this code works fine.

I miss something ? Is there a way to declare the nsIPrincipal ?

Do you think I should file a bug ?

Thanks,

Sylvain