importNode fails with NS_ERROR

This does not seem to be [url]https://bugzilla.mozilla.org/show_bug.cgi?id=460460[/url]
..
One of the documents (original source of the imported node) is created
through:
var parser = Cc["@mozilla.org/xmlextras/domparser;1"].createInstance
(Ci.nsIDOMParserJS);
parser.init(null, uri, uri);
var document = parser.parseFromStream(stream, channel.contentCharset,
stream.available(), "text/xml");

The other one through Cc["@mozilla.org/xml/xml-document;
1"].createInstance(Ci.nsIDOMDocument).implementation.createDocument
("", "root", null).

During addon initialization the node is imported flawlessly, but in
runtime it fails with NS_ERROR_UNEXPECTED. In During runtime this
process is initialized by a button click in the navigator window
(chrome context). But if I try to trigger it with a timer which is set
in the internals of my extension, importNode works.
If I remove parser.init(null, uri, uri) it works again, but it's vital
to pass base uri to the parser. init takes some nsIPrincipal as a
first argument which seems to be responsible for security, so it looks
like some kind of a security problem. Is it a bug or should I really
create this principal and pass it to init to fix the issue?

importNode fails with NS_ERROR_UNEXPECTED