Is this a bug of module struct?

[rong.xian at gmail.com]

Before I was bitten by the difference below, I think these two ways are
the same.
However, they are not.
Is there any geek who can tell me if this is a bug?
(some weird '\x00\x00' was inserted between '0123456789abcd' and 6 )


>>> struct.pack('3I14sI',1,19960101,14,'0123456789abcd',6)
'\x01\x00\x00\x00%\x910\x01\x0e\x00\x00\x000123456789abcd\x00\x00\x06\x00\x00\x00'
>>> struct.pack('3I14s',1,19960101,14,'0123456789abcd')+struct.pack('I',6)
'\x01\x00\x00\x00%\x910\x01\x0e\x00\x00\x000123456789abcd\x06\x00\x00\x00'