This is because by default, the content filter is working, but the action is set to "Take no further action". So, when a message matches the content filter for spam, several email headers are added, and the message is queued for the client.
In this configuration, it's up to your CLIENT to check for the headers, and handle the email appropriately.
What I did was modify the content filter slightly to add the header "X-SRV-SPAM: This message failed the server SPAM test" to each message that ended up with a weight greater than 50. Then, my client (I use Outlook 2003) checks for that header, and if it exists, moves the message to a special folder called "SERVER SPAM". I can then check those messages for false positives, and tweak the content filter on the server as needed to eliminate the false positive.
Note that the default content filter adds the following headers (this is an example from one of my messages)
X-UC-Weight: [# ] 55
X-CC-Diagnostic: Body matches "*http:*.biz*" (15),
Body contains (ob) "viagra" (40)
And this is the header I added:
X-SRV-SPAM: This message failed the Server SPAM test
So you could also look for X-UC_Weight and if the weight is greater than 50, move it to spam... but I added my header to make it easier to check (if X-SRV-SPAM exists, by default, it exceeds a weight of 50).
Hope that helps,
Bill