1. There is special code in the bz2 decoder that returns an empty text str object at EOF, even though bz2-codec is a bytes-to-bytes codec:
>>> import codecs
>>> decoder = codecs.getincrementaldecoder("bz2")()
>>> decoder.decode(codecs.encode(b"data", "bz2"))
b'data'
>>> decoder.decode(b"", final=True)  # Should return bytes object
''

2. The base64 decoder does not handle partial sets of four codes, because it treats each input chunk as a stand-alone base64 encoding:
>>> tuple(codecs.iterdecode((b"AA", b"AA\r\n"), "base64"))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.5/codecs.py", line 1039, in iterdecode
    output = decoder.decode(input)
  File "/usr/lib/python3.5/encodings/base64_codec.py", line 35, in decode
    return base64.decodebytes(input)
  File "/usr/lib/python3.5/base64.py", line 554, in decodebytes
    return binascii.a2b_base64(s)
binascii.Error: Incorrect padding