Does caching work properly for ftp requests?

I am currently running a 1.1.9 prerelease on NEXTSTEP 3.3.

My question is this: ftp://etc URL's are cached by squid. This is fine, but
since there are no expirations for ftp-ed objects, I expect squid to look
if the original has changed every time I request the object. This does not
happen, not even for directories. Or, otherwise stated: once an ftp-object
is cached it seems never to be updated.

Have I concluded this correctly and how would I be able to check the
working of caching ftp URL's?

---
Gerben_Wierda@RnA.nl (Gerben Wierda) NEXTSTEP RD242
"If you don't know where you're going, any road will take you there"
Paraphrased in Alice in Wonderland, originally from the Talmud.
Renee: "Met veel koper maakt men hoempa." (After hearing a Nielsen symphony)