Data all piles up in one directory.

Newbie question:

Given a Squid 2.2 system set up, essentially, according to the Quickstart
instructions, with only one significant modification; I have increased the
'maximum_object_size' to '40 MB'; why would all the cache-data e being
placed in a single cache-directory?

To be more specific, I have noticed that the FAQ says the following about
file-distribution within the cache:

--------------------------
When Squid wants to create a new disk file for storing an object, it first
selects which cache_dir the object will go into. This is done with the
storeDirSelectSwapDir() function. If you have N cache directories, the
function identifies the 3N/4 (75%) of them with the most available space.
These directories are then used, in order of having the most available
space. When Squid has stored one URL to each of the 3N/4 cache_dir's, the
process repeats and storeDirSelectSwapDir() finds a new set of 3N/4 cache
directories with the most available space.
--------------------------

Given that this is the case, after ~2 weeks of operation under moderate
load, with a total of 450MB of space, and a cache_dir line which reads:

--------------------------
cache_dir /squid/cache 400 16 256
--------------------------

why would I be seeing the following behaviour:

--------------------------
endo:/squid/cache> du -sk *
236134 00
260 01
260 02
260 03
260 04
260 05
260 06
260 07
260 08
260 09
260 0A
260 0B
260 0C
260 0D
260 0E
260 0F
1030 swap.state
--------------------------

The cache also appears to be repacing cache data at what seems(to me) to be
a very rapid rate... I will probably understand this better as I read more
of the on-line support documentation.

Is this a known behaviour? Is there some aspect of the configuration which
(given very limited time) I should be paying particular attention to?

Thanks in advance...

--
Thorne Huw Lawler
Verve, Inc.