Test at http://w3c-test.org/webapps/DOMCore/tests/submissions/Ms2ger/Node-cloneNode.html
Why is this a bug? See bug 11646 - the behavior is implementation dependent.
I cannot find that quote in the current DOM spec: http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html
Perhaps the future iteration should be fixed to not be incompatible with current official spec. If you demand throwing an exception where it didn't use to throw - and where authors expect something else - that's just being difficult.
We pass all the cloneNode() tests in https://wpt.fyi/results/dom/nodes. I'm going to assume this got resolved over the intervening years.