See:
http://bugzilla.spamassassin.org/show_bug.cgi?id=4249 http://bugzilla.spamassassin.org/show_bug.cgi?id=3997
It would be interesting to see if folks could try the patches added to the tickets, try a slow DNS resolution (longer than the timeout of 3 seconds) and see if they can duplicate/eliminate the error. Also if the hypothesis on 4249 is correct, then the problem of mixed up UDP packets may show up on a network analyzer, tcpdump, etc.
Jeff C. -- "If it appears in hams, then don't list it."