why does HDB iteritems() decode key and value

[mosasiru]

I use python3.5 and tc 0.7.2.
Why HDB iteritems() decode key and value unlike items()?
Following is an example.

In [160]: db.open("test", tc.HDBOWRITER | tc.HDBOCREAT)
In [162]: db[b"hoge"] = b"fuga"
In [163]: db["ほげ".encode("utf-8")] = "ふが".encode("utf-8")
In [164]: db.items()
Out[164]:
[(b'hoge', b'fuga'),
 (b'\xe3\x81\xbb\xe3\x81\x92', b'\xe3\x81\xb5\xe3\x81\x8c')]

In [165]: list(db.iteritems())
Out[165]: [('hoge', 'fuga'), ('ほげ', 'ふが')]

So I have a trouble with below error when HDB include a value msgpack.packb() value.

In [8]: db[b"hoge"] = msgpack.packb([1,2,3])
In [9]: list(db.itervalues())
Out[9]: [b'\xe3\x81\xb5\xe3\x81\x8c']
In [10]: db.items()
Out[10]: [(b'\xe3\x81\xbb\xe3\x81\x92', b'\xe3\x81\xb5\xe3\x81\x8c')]
In [11]: list(db.iteritems())
---------------------------------------------------------------------------
UnicodeDecodeError                        Traceback (most recent call last)
<ipython-input-10-9453a76d2e05> in <module>()
----> 1 list(db.iteritems())
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x93 in position 0: invalid start byte