Overwrite of alpha values when casting a string slice to int (Trac #2005) #2598

>>> B = np.zeros((5,3)).astype('S10')
>>> B[:,0] = range(5)
>>> B[0,0] = 'StudentID'
>>> B
array([['StudentID', '0.0', '0.0'],
       ['1', '0.0', '0.0'],
       ['2', '0.0', '0.0'],
       ['3', '0.0', '0.0'],
       ['4', '0.0', '0.0']], 
      dtype='|S10')

# Casting the whole array to int throws an error, as it should.
>>> B.astype(int)

Traceback (most recent call last):
  File "<pyshell#152>", line 1, in <module>
    B.astype(int)
ValueError: invalid literal for int() with base 10: 'StudentID'

# However, casting a slice of the same array to int actually changes 'StudentID' into an integer (11 in this case).
>>> B[:,0].astype(int)
array([11,  1,  2,  3,  4])
>>>