[CentOS] LVM filters not working?

Hi, I'm trying to set up a redundant DRBD system but I'm running into trouble when I try to define a volume group. The physical backing device for the drbd resource /dev/drbd0 is /dev/vdb1. The problem is that when I do a "pvs" on the command line the physical volume is shown as /dev/vdb1. So I tried the following filter in /etc/lvm/lvm.conf:

filter = [ "r|/dev/vdb.*|", "a/.*/"

But this doesn't seem to haven any effect at all. The system still sees the volumen group on /dev/vdb1. Also various how-to's on the net say I should pay attention to deleting /etc/lvm/cache/.cache which makes sense but this file is never created.

Any ideas what might be going on here? I'm trying all of this on CentOS 6.

Regards, Dennis