Description of problem:
This feature may just need better documentation for better understanding. Howeve, the way I understand this feature, the following set up should produce a mirror with each leg using devices with only similarly tagged devices.

# This is the cling config in lvm.conf:
     cling_tag_list = [ "A", "B" ]

[root@taft-03 ~]# pvs -a -o +pv_tags /dev/sd[bcdefgh]1
  PV         VG   Fmt  Attr PSize   PFree   PV Tags
  /dev/sdb1  taft lvm2 a-   135.66g 135.66g A
  /dev/sdc1  taft lvm2 a-   135.66g 135.66g B
  /dev/sdd1  taft lvm2 a-   135.66g 135.66g B
  /dev/sde1  taft lvm2 a-   135.66g 135.66g C
  /dev/sdf1  taft lvm2 a-   135.66g 135.66g C
  /dev/sdg1  taft lvm2 a-   135.66g 135.66g A
  /dev/sdh1  taft lvm2 a-   135.66g 135.66g A


[root@taft-03 ~]# lvcreate --alloc cling -m 1 -n mirror -L 200G --nosync taft
  WARNING: New mirror won't be synchronised. Don't read what you didn't write!
  Logical volume "mirror" created


[root@taft-03 ~]# lvs -a -o +devices
 LV                VG        Attr   LSize   Log         Copy%  Devices
 mirror            taft      Mwl-a- 200.00g mirror_mlog 100.00 mirror_mimage_0(0),mirror_mimage_1(0)
 [mirror_mimage_0] taft      iwi-ao 200.00g                    /dev/sdb1(0)
 [mirror_mimage_0] taft      iwi-ao 200.00g                    /dev/sdc1(0)
 [mirror_mimage_1] taft      iwi-ao 200.00g                    /dev/sdd1(0)
 [mirror_mimage_1] taft      iwi-ao 200.00g                    /dev/sde1(0)
 [mirror_mlog]     taft      lwl-ao   4.00m                    /dev/sdc1(16470)

Shouldn't the above leg mimage_0 have been made up of devices with tag "A" (/dev/sd[bgh]1) and leg mimage_1 of devices with tag "B" (/dev/sd[cd]1)? 


Version-Release number of selected component (if applicable):
2.6.32-94.el6.x86_64

lvm2-2.02.83-2.el6    BUILT: Tue Feb  8 10:10:57 CST 2011
lvm2-libs-2.02.83-2.el6    BUILT: Tue Feb  8 10:10:57 CST 2011
lvm2-cluster-2.02.83-2.el6    BUILT: Tue Feb  8 10:10:57 CST 2011
udev-147-2.31.el6    BUILT: Wed Jan 26 05:39:15 CST 2011
device-mapper-1.02.62-2.el6    BUILT: Tue Feb  8 10:10:57 CST 2011
device-mapper-libs-1.02.62-2.el6    BUILT: Tue Feb  8 10:10:57 CST 2011
device-mapper-event-1.02.62-2.el6    BUILT: Tue Feb  8 10:10:57 CST 2011
device-mapper-event-libs-1.02.62-2.el6    BUILT: Tue Feb  8 10:10:57 CST 2011
cmirror-2.02.83-2.el6    BUILT: Tue Feb  8 10:10:57 CST 2011


How reproducible:
Everytime