Upon further investigation, it looks like this may be related to an upgrade of libnet-dns-perl from 0.81-2+b1 to 1.05-1.
See upstream https://bz.apache.org/SpamAssassin/show_bug.cgi?id=7231 Upstream says the bug is closed. I guess I have to wait for the next version of spamassassin. Also, this might be the same as bug# 794877 Marc
