Sieve Not Functioning Correctly

[Raymond Sundland]

Hello,

To start, my setup:

Postfix 2.x calling SpamAssassin's spamc which calls Cyrus 2.2's (ALPHA) 
deliver.

As some of you may know, when SpamAssassin sees spam (when it meets a 
certain level), it creates the header X-Spam-Flag and sets it to YES.  I 
have created a sieve filter which looks for the X-Spam-Flag and sees if 
it is YES, and if it is, it should move the mail to another mailbox.

However, it does not work... I do not know why, and can not figure out 
why.  Sieve *does* work... in fact, it doesn't seem to work on headers 
at all.  If I want to do matching, it's against the Sender address... if 
I do something like List-Id, it won't work.

imapd.conf sieve config stuff:

# sieve
sievedir: /var/imap/sieve
sieve_maxscriptsize: 32
sieve_maxscripts: 25

Any help would be appreciated.  (FYI. I've done mail list searches and 
found nothing, so if there is one, if you could link, it would be 
appreciated.

Thanks.