This exists in the latest 5.8 rpms as well.

2.6.18-274.el5

lvm2-2.02.88-4.el5    BUILT: Wed Nov 16 09:40:55 CST 2011
lvm2-cluster-2.02.88-4.el5    BUILT: Wed Nov 16 09:46:51 CST 2011
device-mapper-1.02.67-2.el5    BUILT: Mon Oct 17 08:31:56 CDT 2011
device-mapper-event-1.02.67-2.el5    BUILT: Mon Oct 17 08:31:56 CDT 2011
cmirror-1.1.39-10.el5    BUILT: Wed Sep  8 16:32:05 CDT 2010
kmod-cmirror-0.1.22-3.el5    BUILT: Tue Dec 22 13:39:47 CST 2009


[root@grant-01 ~]# pvscan
  PV /dev/sdb1   VG seven        lvm2 [68.11 GB / 68.02 GB free]
  PV /dev/sdc3   VG seven        lvm2 [90.82 GB / 90.72 GB free]
  PV /dev/sdc2   VG seven        lvm2 [90.82 GB / 90.82 GB free]
  PV /dev/sdc1   VG seven        lvm2 [90.82 GB / 90.82 GB free]
  PV /dev/sdb2   VG seven        lvm2 [68.11 GB / 68.11 GB free]

[root@grant-01 ~]# lvs -a -o +devices
  LV                   VG     Attr   LSize   Log       Devices
  rlog                 seven  mwi--- 100.00M rlog_mlog
rlog_mimage_0(0),rlog_mimage_1(0)
  [rlog_mimage_0]      seven  Iwi--- 100.00M           /dev/sdb1(0)
  [rlog_mimage_1]      seven  Iwi--- 100.00M           /dev/sdc3(0)
  [rlog_mlog]          seven  mwi---   4.00M          
rlog_mlog_mimage_0(0),rlog_mlog_mimage_1(0)
  [rlog_mlog_mimage_0] seven  Iwi---   4.00M           /dev/sdc1(0)
  [rlog_mlog_mimage_1] seven  Iwi---   4.00M           /dev/sdb2(0)

[root@grant-01 ~]# vgsplit -n rlog seven ten
  Can't split mirror rlog between two Volume Groups

Created attachment 535200 [details]
RHEL5.8 port of upstream patch

Fixed in lvm2-2.02.88-5.el5.

Fix verified in the latest rpms.

2.6.18-274.el5

lvm2-2.02.88-5.el5    BUILT: Fri Dec  2 12:25:45 CST 2011
lvm2-cluster-2.02.88-5.el5    BUILT: Fri Dec  2 12:48:37 CST 2011
device-mapper-1.02.67-2.el5    BUILT: Mon Oct 17 08:31:56 CDT 2011
device-mapper-event-1.02.67-2.el5    BUILT: Mon Oct 17 08:31:56 CDT 2011
cmirror-1.1.39-10.el5    BUILT: Wed Sep  8 16:32:05 CDT 2010
kmod-cmirror-0.1.22-3.el5    BUILT: Tue Dec 22 13:39:47 CST 2009


SCENARIO - [split_rlog_mirror_lv]
Split out a redundant log mirrored lv on grant-01
free pvs for grant-01: /dev/sdb1 /dev/sdc2 /dev/sdc1 /dev/sdc3 /dev/sdb2
create a redundant log mirror
deactivating seven/rlog
grant-01: vgsplit -n rlog seven ten
Deactivating and removing volume groups...  


SCENARIO - [split_rlog_mirror_pvs]
Split out pvs of a redundant log mirror on grant-01
free pvs for grant-01: /dev/sdb2 /dev/sdc2 /dev/sdc3 /dev/sdb1 /dev/sdc1
create a redundant log mirror
deactivating seven/rlog
grant-01: vgsplit seven ten /dev/sdb2 /dev/sdc2 /dev/sdc3
Deactivating and removing volume groups...

    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
vgsplit is now able to split a volume group containing a mirror with mirrored logs.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2012-0161.html