savecore: can't find device

Does anyone know if there are potentially undocumented issues with
savecore(8) when using swap on LVM volumes on top of CGD?

# savecore -n
savecore: can't find device 194/1


Swap volume is enabled and active:
# grep swap /etc/fstab
/dev/vg0/swap     none        swap      sw,dp             0 0

# swapctl -l
Device        1K-blocks     Used    Avail Capacity  Priority
/dev/vg0/swap   2097152        0  2097152     0%    0


Running kernel also matches:
# sysctl machdep.booted_kernel
machdep.booted_kernel = netbsd_test

# ls -l /netbsd_test
-rwxr-xr-x  1 root  wheel  30031216 Mar  8 10:59 /netbsd_test


The /dev/vg0/* are symlinks to /dev/mapper/* and device numbers for
rvg0-swap match 194,1. I can also read OK with dd from this device:
# ls -l /dev/mapper/*swap*
crw-r-----  1 root  operator  194, 1 May 20 08:05 /dev/mapper/rvg0-swap
brw-r-----  1 root  operator  169, 1 May 20 08:05 /dev/mapper/vg0-swap

# dd if=/dev/mapper/rvg0-swap of=/dev/null bs=64k count=1
1+0 records in
1+0 records out
65536 bytes transferred in 0.005 secs (13107200 bytes/sec)