I'm the maintainer of mandrake mailman package. I have a bug report about wrong perms for logs files, see: http://qa.mandrakesoft.com/show_bug.cgi?id=9319
Even if I changed layout drastically to achieve FHS compliance, this kind of problem is quite curious. Those files are created at run-time, and I guess the various scripts take care of ensuring correct perms, whereas group ownership is ensured by the setgid bit for the log directory. For instance, smtp and qrunner log files are OK. So, what could have get wrong here ?