Looking at the test case 'test_from_buffer_copy' here:
https://github.com/python/cpython/blob/master/Lib/ctypes/test/test_frombuffer.py

This suggests the failure to call init in this instance is expected behavior (similarly for from_buffer), unlike e.g. the classmethod fromkeys() with a dictionary subclass which behaves as expected.

Are there any required changes here, perhaps if not code then documentation?