I've just checked a spam that made it into my Inbox, and the headers do contain Spam headers; perhaps I'm not having the same problem, and it's just coincidental that I'm getting an influx of new spam. Interesting note: no spam is being redirected to Junk -- all of it gets delivered to my inbox. Hmm...
X-Virus-Scanned: amavisd-new at divergentsystems.net
X-Amavis-Alert: BAD HEADER SECTION, Non-encoded 8-bit data (char E2 hex):
Subject: don\342\200\231t spend valen[...]
X-Spam-Status: No, score=5.98 tagged_above=-10 required=6.6 tests=[BAYES_80=2,
HTML_IMAGE_ONLY_24=1.618, HTML_MESSAGE=0.001, RDNS_NONE=0.793,