I presume you claim the dict example to be a bug in relation to "A class
that has a metaclass derived from ABCMeta cannot be instantiated unless
all of its abstract methods and properties are overridden."

There is the same difference with @abstractproperty
Windows, 3.0.1

class C(metaclass=abc.ABCMeta):
	@abc.abstractmethod
	def f(self): return True

class C2(dict,metaclass=abc.ABCMeta):
	@abc.abstractmethod
	def f(self): return True

c2=C2()
print(c2.f())

c=C()
# prints
True
...
TypeError: Can't instantiate abstract class C with abstract methods f