Bug in struct.pack?

[Alex Stapleton]

from struct import pack
 >>> pack("B", 1)
'\x01'
 >>> pack("BB", 0, 1)
'\x00\x01'
 >>> pack("BI", 0, 1)
'\x00\x00\x00\x00\x01\x00\x00\x00'
 >>> calcsize("BI")
8
 >>> calcsize("BB")
2

Why does an unsigned char suddenly become 4 bytes long when you  
include an unsigned int in the format string? It's consistent  
behaviour but it's incorrect.

Also.

 >>> calcsize('BL')
8
 >>> calcsize('BBL')
8
 >>> calcsize('BBBL')
8
 >>> calcsize('BBBBL')
8
 >>> calcsize('BBBBBL')
12
 >>> pack("BBBL", 255,255,255,0)
'\xff\xff\xff\x00\x00\x00\x00\x00' ####### That's 3 255's and 5(!?!?)  
0's
 >>> pack("BBBBL", 255,255,255,255,0)
'\xff\xff\xff\xff\x00\x00\x00\x00' ######### 4 255's and 4 0's!

Which is all kinds of wrong.

BL should be 9
BBL should be 10
....

Python 2.4.1 (#2, May  5 2005, 11:32:06)
[GCC 3.3.5 (Debian 1:3.3.5-12)] on linux2

Same behaviour on my PowerBook using

Python 2.3.5 (#1, Mar 20 2005, 20:38:20)
[GCC 3.3 20030304 (Apple Computer, Inc. build 1809)] on darwin

sizeof(unsigned long) should be 8 on both of these platforms
sizeof(unsigned char) should be 1 on both as well

So am I just being stupid and not specifying something I should be?  
Or is struct really that broken?