Duplicate Mailman postings, mailman unpickling error in some conditions

After applying the most recent Security Update to our Mac OS X Server 10.4.10 installation, we are encountering the following two problems:

1) Each message sent to any of our Mailman-based e-mail lists appears to be sent in duplicate to each member of the list

2) Under some conditions we encounter an "unpickling error" that from Googling around would appear to be a python error, as follows:

Aug 03 01:22:25 2007 (7442) Uncaught runner exception: invalid load key, 'm'.
Aug 03 01:22:25 2007 (7442) Traceback (most recent call last):
File "/usr/share/mailman/Mailman/Queue/Runner.py", line 111, in _oneloop
self._onefile(msg, msgdata)
File "/usr/share/mailman/Mailman/Queue/Runner.py", line 167, in _onefile
keepqueued = self._dispose(mlist, msg, msgdata)
File "/usr/share/mailman/Mailman/Queue/IncomingRunner.py", line 130, in _dispose
more = self._dopipeline(mlist, msg, msgdata, pipeline)
File "/usr/share/mailman/Mailman/Queue/IncomingRunner.py", line 153, in _dopipeline
sys.modules[modname].process(mlist, msg, msgdata)
File "/usr/share/mailman/Mailman/Handlers/Moderate.py", line 109, in process
Hold.hold forapproval(mlist, msg, msgdata, Hold.NonMemberPost)
File "/usr/share/mailman/Mailman/Handlers/Hold.py", line 214, in hold forapproval
id = mlist.HoldMessage(msg, reason, msgdata)
File "/usr/share/mailman/Mailman/ListAdmin.py", line 178, in HoldMessage
self.__opendb()
File "/usr/share/mailman/Mailman/ListAdmin.py", line 80, in __opendb
self.__db = cPickle.load(fp)
UnpicklingError: invalid load key, 'm'.

Aug 03 01:22:25 2007 (7442) SHUNTING: 1186122145.370055+f2ab5fac4a7b2dc159498a36ed5c91b5de42f490

The condition that produced this particular error involved sending a message to the mailman list on our server.

Any advice from anyone on either of these two problems? Is it possible that the security update left an old copy of mailman around with a different python, or is this a bug in the copy of mailman that we have in effect after the update?

We have tried disabling and re-enabling the mailing lists under Server Admin, stopping and starting the Mail service entirely, rebooting, stopping and starting mailman using mailmanctl from the command line, stopping mailman and running the check_db and check-perms commands and then re-enabling it, all to no avail. Help would be much appreciated.