importNode doesn't work in IE - cloneNode is the only way to copy a node afaik.
It might be related the strangeness of accessing the document in the first place - IE has contentWindow.document when it's an iframe, but an <object> has no contentWindow, and IE doesn't support contentDocument, so the only way I could find to get the document is with a reference to the <object> itself. Like this example, trying to copy individual <ul> nodes out of another element in the embedded document:
var obj = document.getElementById("someObject");
var doc = obj;
var docElement = doc.getElementById("whatever");
var docTree = docElement.getElementsByTagName('ul');
var docUL = docTree.cloneNode(true)
Then query the parentNode of docTree - it's a document fragment; try to append or move the docTree node - you can't, because it isn't really a node.