FTP cacheing doesn't seem to work on squid-2.2.STABLE4-8

I have noticed for some time that FTP caching doesn't seem to work on
squid-2.2.STABLE4-8.

Here's the scenario

[stephenm@mcfeast stephenm]$ wget
ftp://ftp.mozilla.org/pub/mozilla/nightly/latest/mozilla-i686-pc-linux-gnu.tar.gz

--09:43:51--
ftp://ftp.mozilla.org:21/pub/mozilla/nightly/latest/mozilla-i686-pc-linux-gnu.tar.gz

           => `mozilla-i686-pc-linux-gnu.tar.gz.1'
Connecting to squid:3128... connected!
Proxy request sent, awaiting response... 200 OK
Length: 5,288,426 [application/x-tar]

Do this twice in a row and you get two complete downloads

here is the store.log
[root@squid squid]# grep -1
ftp://ftp.mozilla.org/pub/mozilla/nightly/latest/mozilla-i686-pc-linux-gnu.tar.gz
store.log
941944786.220 SWAPOUT 00008473 200 941944522 941876735 -1
text/html 10859/10859 GET http://www.mozilla.org/
941946379.624 SWAPOUT 00008480 200 941286910 941909548 -1
application/x-tar 5203546/5203546 GET
ftp://ftp.mozilla.org/pub/mozilla/nightly/latest/mozilla-i686-pc-linux-gnu.tar.gz

941946553.182 SWAPOUT 00008482 200 941214522 941179320 -1
text/html 26553/26553 GET
http://www.infocom.cqu.edu.au/Units/win99/85202/

--
942114248.451 RELEASE FFFFFFFF  200        -1        -1        -1
text/html -1/1003 GET http://chat.teen.com/eshare/server?
942114249.206 SWAPOUT 0001022F  200 941455535 942081843        -1
application/x-tar 5287905/5287905 GET
ftp://ftp.mozilla.org/pub/mozilla/nightly/latest/mozilla-i686-pc-linux-gnu.tar.gz
942114250.039 RELEASE FFFFFFFF  302 942113989        -1 942114249
text/html 36/36 GET
http://ad.doubleclick.net/ad/www.shift.com/std-map.html;ord=942113350508?
--
942187796.222 RELEASE FFFFFFFF  302 942187445        -1        -1
text/html 163/163 GET http://www.standards.com.au/information-sheets
942187797.962 SWAPOUT 00013956  200 941529216 942177203        -1
application/x-tar 5288426/5288426 GET
ftp://ftp.mozilla.org/pub/mozilla/nightly/latest/mozilla-i686-pc-linux-gnu.tar.gz
942187798.824 SWAPOUT 0001395C  200 942187447 936768133        -1
text/html 4185/4185 GET http://www.standards.com.au/information-sheets/
[root@squid squid]#
How come this doesn't cache?
Thanks
Stephen Moore