Help mp3 attachment

[John Fleming]

I run a very simple Postfix - Procmail - SpamAssassin - CLamAV setup that 
has been working great, but tonight I see something I don't understand. 
Look at the 2 examples below please.  Both messages got virus-scanned. 
However, the message that includes an mp3 audio attachment, appears that it 
didn't get spam-scanned at all, whereas a totally plain message does.  Can 
anyone explain this?  What attachment property would cause the message not 
to pass to spamd at all?  Thanks - John

Plain message with 500K mp3 attachment:
X-Virus-Status: No
X-Virus-Checker-Version: Luke wa9als.com running clamassassin 1.2.1 with 
ClamAV 0.85/879/Sun May 15 08:43:45 2005 signatures 31.879
Status:
X-Antivirus: AVG for E-mail 7.0.308 [266.11.10]
Mime-Version: 1.0
Content-Type: multipart/mixed; 
boundary="----=_NextPart_000_0050_01C5599C.1DDB9FF0"


Plain message without attachment:
X-Virus-Status: No
X-Virus-Checker-Version: Luke wa9als.com running clamassassin 1.2.1 with 
ClamAV 0.85/879/Sun May 15 08:43:45 2005 signatures 31.879
X-Spam-Checker-Version: SpamAssassin 3.0.2 (2004-11-16) on Luke.wa9als.com
X-Spam-Level:
X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00 autolearn=ham
version=3.0.2
Status:
X-Antivirus: AVG for E-mail 7.0.308 [266.11.10]
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; format=flowed; charset=iso-8859-1; 
reply-type=original


--
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.308 / Virus Database: 266.11.10 - Release Date: 5/13/2005