Why does not changing one bit in the key or the initial value of Triple DES does not produce different encrypted data?

Question

I use pyDes to encrypt some data. I would like to demonstrate that if you change at least one bit in a key or initial value, the encrypted data will be completely different. I set a 16-byte key to change the last character to +/- 1, resulting in at least one bit different. However, even when I do this, three different instances of encrypted data are not all different.

from pyDes import *

data = 'Hello'

# CBC : Cipher-Block-Chaining
# \0..\1: arbitrary initial value for CBC
# pad=None: let pyDes take care of padding bytes
k1 = triple_des("16-byte-key-here", CBC, "\0\0\0\0\0\0\0\1", pad=None, padmode=PAD_PKCS5)
k2 = triple_des("16-byte-key-herf", CBC, "\0\0\0\0\0\0\0\1", pad=None, padmode=PAD_PKCS5)
k3 = triple_des("16-byte-key-herd", CBC, "\0\0\0\0\0\0\0\1", pad=None, padmode=PAD_PKCS5)

d1 = k1.encrypt(data)
d2 = k2.encrypt(data)
d3 = k3.encrypt(data)

assert d1 != d2
assert d2 != d3
assert d1 != d3

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Answer 1

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