I've just released Mailman 2.0 beta 5. This is an important bug fix release that should once and for all solve the "cookie re-authentication" bug. It also fixes a small security hole that could be exploited by clever local users to gain group mailman permission.
As usual, you can get the tarball from SourceForge
or (soon) ftp.gnu.org
Please let me know how it goes for you. Remember to use the SourceForge bug tracker for reporting bugs NOT the old Jitterbug database on python.org (which I cannot shut off right now). Also, patches should be uploaded to the SourceForge patch manager.