Mailman/postfix problem

["Will Twomey" <termina@gmail.com>]

I installed both postfix and mailman with apt-get.

Everything was working well, until about a week ago when I did apt-get
update/upgrade.

I'm running Debian stable.

When I try to send an email to mailman@mydomain.com (which used to
work), I see this in /var/log/mail.err (and mail.log)

Mar 22 13:08:59 csc Mailman mail-wrapper: Group mismatch error. 
Mailman expected the mail wrapper script to be executed as group
"daemon", but the system's mail server executed the mail script as
group "postfix".  Try tweaking the mail server to run the script as
group "daemon", or re-run configure,  providing the command line
option `--with-mail-gid=postfix'.

Since I didn't compile these from source, how can I fix this problem?
Why would apt have broken this?

I've used the 'check_perms' script, and nothing is wrong with the permissions.

postfix check also shows nothing wrong

Thanks
--
Will Twomey
http://UnhandledExceptions.com