Does anyone else notice the following?

With a family and a busy schedule, my inbox is currently at 896 items and 694 unread. I don't think this has anything to do with my problem, because I did not notice it before the SPAM program changed branding. But here's what I am experiencing:

I bring up Outlook 2003 and ZA Anti-Spam scans my Inbox. It takes a few minutes, but nothing new found.

After a few moments, Outlook connects to my mail servers and downloads my mail (SMTP and POP-3). Anti-Spam finds the mandatory one or two new SPAM messages out of the 50-60 messages downloaded across 5 mail servers / accounts.

Then, I scan the current folder - Inbox. Anti-Spam finds 15-20 new suspicious messages.

Why do the first two "Scans" not find what is found when I manually scan Inbox?

Outlook 2003, fully patched
ZA Suite, 7.0.462.000
AntiSpam version 5.0.6.8903

Operating System:Windows XP Pro
Software Version:7.0
Product Name:ZoneAlarm Internet Security Suite