Description of problem:
This sort of operation used to be protected against, which makes me believe this is a regression.

[root@grant-03 ~]# lvcreate --yes -n fs_to_mirror -L 1.5G mirror_sanity
Logical volume "fs_to_mirror" created.
[root@grant-03 ~]# lvs -a -o +devices
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert Devices
fs_to_mirror mirror_sanity wi-a---- 1.50g /dev/nvme0n1p1(0)

[root@grant-03 ~]# lvconvert --type mirror -m 1 mirror_sanity/fs_to_mirror &
[1] 1560199
[root@grant-03 ~]#
Logical volume mirror_sanity/fs_to_mirror being converted.
mirror_sanity/fs_to_mirror: Converted: 3.12%
ABORTING: Mirror percentage check failed.

[1]+ Exit 5 lvconvert --type mirror -m 1 mirror_sanity/fs_to_mirror

<WHILE ABOVE CMD IS RUNNING>
[root@grant-03 ~]# lvconvert --splitmirrors 1 --name new mirror_sanity/fs_to_mirror
Logical volume mirror_sanity/fs_to_mirror converted.

[root@grant-03 ~]# lvs -a -o +devices
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert Devices
fs_to_mirror mirror_sanity wi-a---- 1.50g /dev/nvme0n1p1(0)
new mirror_sanity wi-a---- 1.50g /dev/nvme1n1p1(0)

May 11 18:31:15 grant-03 systemd[1]: Started LVM2 poll daemon.
May 11 18:31:16 grant-03 dmeventd[1559481]: mirror_sanity-fs_to_mirror is now in-sync.
May 11 18:31:20 grant-03 dmeventd[1559481]: No longer monitoring mirror device mirror_sanity-fs_to_mirror for events.
May 11 18:31:30 grant-03 lvmpolld[1560234]: W: #011LVPOLL: PID 1560237: STDERR: ' ABORTING: Mirror percentage check failed.'
May 11 18:31:30 grant-03 lvmpolld[1560234]: LVMPOLLD: lvm2 cmd (PID 1560237) failed (retcode: 5)
May 11 18:32:30 grant-03 systemd[1]: lvm2-lvmpolld.service: Deactivated successfully.

Version-Release number of selected component (if applicable):
kernel-5.14.0-284.11.1.el9_2 BUILT: Wed Apr 12 04:16:55 PM CEST 2023
lvm2-2.03.21-1.el9 BUILT: Fri Apr 21 02:33:33 PM CEST 2023
lvm2-libs-2.03.21-1.el9 BUILT: Fri Apr 21 02:33:33 PM CEST 2023

How reproducible:
Everytime