Mailman mail-wrapper: Group mismatch error. after aptitude updates on 8/24/2015

Ubuntu 12.04 LTS system in operation. Mailman lists were working prior to doing updates with aptitude. After running updates on 8/24/2015, mailman stopped working. mail.log shows, e.g.:

Aug 26 11:06:01 eclogite sm-mta[27095]: t7QF60VP027095: Milter accept: message
Aug 26 11:06:01 eclogite Mailman mail-wrapper: Group mismatch error. Mailman expected the mail#012wrapper script to be executed as group "daemon", but#012the system's mail server executed the mail script as#012group "smmsp". Try tweaking the mail server to run the#012script as group "daemon", or re-run configure, #012providing the command line option `--with-mail-gid=smmsp'.
Aug 26 11:06:01 eclogite sm-mta[27096]: t7QF60VP027095: to="|/var/lib/mailman/mail/mailman post probeusers", ctladdr=<email address hidden> (116/0), delay=00:00:00, xdelay=00:00:00, mailer=prog, pri=31648, dsn=5.3.0, stat=unknown mailer error 2
Aug 26 11:06:01 eclogite sm-mta[27096]: t7QF60VP027095: t7QF61VO027096: DSN: unknown mailer error 2

Since mailman and all the components of the mail system are aptitude packages, fixing it from my end is not elementary. Subsequent aptitude updates would likely break anything I tried to fix.

The specific updates that were run on 8/24/2015 were as follows:

chrisho@eclogite:~$ sudo aptitude upgrade
Resolving dependencies...
The following NEW packages will be installed:
  linux-headers-3.2.0-89{a} linux-headers-3.2.0-89-generic{a} linux-image-3.2.0-89-generic{a}
The following packages will be upgraded:
  libsnmp-base libsnmp-perl libsnmp15 linux-headers-server linux-image-server linux-libc-dev linux-server openssh-client openssh-server tzdata
10 packages upgraded, 3 newly installed, 0 to remove and 0 not upgraded.
Need to get 55.7 MB of archives. After unpacking 218 MB will be used.
Do you want to continue? [Y/n/?] y

(followed by a reboot)

I don't know quite how that connects with sendmail and/or mailman, but it is the only thing that changed about the system.

mailman is:

chrisho@eclogite:~$ aptitude show mailman
Package: mailman
State: installed
Automatically installed: no
Version: 1:2.1.14-3ubuntu0.2

sendmail is:

chrisho@eclogite:~$ aptitude show sendmail
Package: sendmail
State: installed
Automatically installed: no
Version: 8.14.4-2ubuntu2.1

Ubuntu is:

chrisho@eclogite:~$ lsb_release -rd
Description: Ubuntu 12.04.5 LTS
Release: 12.04

We run aptitude update and upgrade routinely, so everything should be at the latest for 12.04 LTS.