This is actually three bugs which are related: Due to a typo, the code in isEqualNode doesn't check if the attributes differ. When fixing this, one of the DOM3 tests started failing. This is because the tests load documents by loading them in a frame/iframe (I'm not sure) and then cloning the document manually. In this code, there's a call to setAttributeNS which sets the namespaceURI to 'null', so it won't be the same as the original.
*** This bug has been marked as a duplicate of 5725 ***
Mass moving XML DOM bugs to the "DOM" Component.