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I don't think it was ever intended that decorators be chained together. 
The whole point is to control binding behavior during dotted look-up (when __getattribute__ is called) and not in other circumstances (such as a direct lookup in a class dictionary).
Note that classmethods typically wrap regular functions which have both __call__ and __get__ methods. The classmethod object intentionally invokes the former instead of the latter which would unhelpfully create an inner bound or unbound method.