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The issue can be reproduced as follows.
import pyarrow as pa
import numpy as np
t = np.datetime64(datetime.datetime.now())
print(type(t), t) # <class 'numpy.datetime64'> 2017-09-30T09:50:46.089952
t_new = pa.deserialize(pa.serialize(t).to_buffer())
print(type(t_new), t_new) # <class 'int'> 0