nditer doesn't preserve the class

nditer_bug.py

import numpy as np
class CustomArray(np.ndarray):
    def __new__(cls, matrix, custom_attribute):
        obj = np.asarray(matrix).view(cls)
        obj.custom_attribute = custom_attribute
        return obj

    def __array_finalize__(self, obj):
        if obj is None:
            return
        self.custom_attribute = getattr(obj, 'custom_attribute', None)

x = CustomArray(np.asarray([1,2,3]), 'some_value')  # a custom array
y = np.asarray([4,5,6])  # a regular array
bar = np.nditer([x, x])[0]
print(type(bar))