numpy.lib.stride_tricks.as_strided() does not preserve some structured dtypes

[fjarri]

In the commit 2293b43 a test for numpy.lib.stride_tricks.as_strided() was added in array.py checking that it preserves a structured dtype. It works for the rather simple type there, but stops working for types with padding set through offsets parameter:

import numpy
from numpy.lib.stride_tricks import as_strided

dtype = numpy.dtype({
    'names':['i1','nested','i2'],
    'formats':['<u4',[('v', '<u8')],'<u4'],
    'offsets':[0,8,16], 'itemsize':24})

arr = numpy.zeros((128,), dtype)

print(dtype)
print(new_arr.dtype)

Output:

{'names':['i1','nested','i2'], 'formats':['<u4',[('v', '<u8')],'<u4'], 'offsets':[0,8,16], 'itemsize':24}
[('i1', '<u4'), ('f1', 'V4'), ('nested', [('v', '<u8')]), ('i2', '<u4'), ('f4', 'V4')]

Apparently, as_strided() adds some dummy fields in this case and removes offsets. The alternative version of as_strided() in array.py does preserve them, but since the numpy one passes the test, it does not get invoked.

Is it the planned behavior?