The copy module uses the same __reduce__ protocol, but reconstruct the object in different order, first set state, then add items. This discrepancy causes a difference between results of pickle/unpickle and copy operations. Example:

>>> class L(list):
...     def __getstate__(self):
...         return list(self)
...     def __setstate__(self, state):
...         self[:] = state
... 
>>> import copy, pickle
>>> pickle.loads(pickle.dumps(L([1, 2])))
[1, 2]
>>> copy.deepcopy(L([1, 2]))
[1, 2, 1, 2]

This was happened with xml.dom.minicompat.NodeList (issue10131).

Definitely one of pickle's or copy's behavior should be changed. But what?