Comment # 3 on bug 1165107 from Klaus Singvogel

I fixed it by myself.
The solution was to call: /usr/lib/mailman/bin/check_perms -f

This changed a lot of permissions and ownership in my system (can't recall
them).

Interesting enough:
I did this before mailman update from May, 12th.

After installation of mailman-2.1.29-lp151.3.11.1 update I performed again:
    /usr/lib/mailman/bin/check_perms -f
...and again a few permissions and ownership were changed in my system.

I think these changes were introduced by the package and wonder about this
discrepancy between tool and package.