After arch installation I edited my /etc/devfsd.conf to the appropriate permission settings but this didn't impress devfs much. After each reboot the old permissions are used again, unless I do a
killall -HUP devfsd
to inform devfsd to reread its configuration. Then all permissions are set as defined in /etc/devfsd.conf.
With demesg I checked that devfsd is started (it is, otherwise the killall command as described above would not have worked) at bootup.
Thanks for all hints and clues.
Don't know if it will help, but you might want to consider upgrading to udev, as devfs is all but history, and this includes the Arch distribution:
If you want to upgrade, here's a udev howto that might help:
I think upgrading might fix your problems. Let us know...