a) 0.75.0-20 doesn't fix ANYTHING. It just adds a cryptic note to a NEWS file burried in /usr/share/doc . The existing /etc/courier/maildroprc rule file is not moved (is conversion needed?) to /etc/maildroprc .
b) How shall admins affected by this handle the tons of email that ended up in /var/spool/mail/<user> to get it delivered using the fixed maildrop rules? courier has no command do read mailspool files and pipe them through the delivery pipeline.