grub-probe fails in the presence of snapshot logical volumes

Here is the output of: grub-probe -d -vv --target=fs_uuid --device /dev/mapper/rover3-saucy--save

I initially thought that this was due to the LVM metadata parsing improvements in 2.02~beta2, but upon inspection the low-level tools were producing the same results in both 2.00 and 2.02~beta2. In fact this bug was introduced by 55e706c918922def17f5012c23cfe88c4c645208, which caused /etc/grub.d/30_os-prober to fail if --target=fs_uuid fails. I'll make it tolerate this instead, which is closer to what it did before.

This bug was fixed in the package grub2 - 2.02~beta2-9

---------------
grub2 (2.02~beta2-9) unstable; urgency=medium

  * Backport from upstream:
    - Tolerate devices with no filesystem UUID returned by os-prober
      (LP: #1287436).

 -- Colin Watson <email address hidden> Thu, 10 Apr 2014 17:34:44 +0100

I have similar issue on Ubuntu 12.04 when running an "apt-get dist-upgrade"...

At some point iI get an output very similar to the reproduced:

root@dcmilphlum173:~# grub-mkconfig -o /boot/grub/grub.cfg
Generating grub.cfg ...
Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.
Found linux image: /boot/vmlinuz-3.2.0-80-generic
Found initrd image: /boot/initrd.img-3.2.0-80-generic
Found linux image: /boot/vmlinuz-2.6.32-73-generic
Found initrd image: /boot/initrd.img-2.6.32-73-generic
Found memtest86+ image: /memtest86+.bin
rmdir: failed to remove `/var/lib/os-prober/mount': Device or resource busy
rmdir: failed to remove `/var/lib/os-prober/mount': Device or resource busy
grub-probe: error: unknown filesystem.
grub-probe: error: unknown filesystem.
done

The below 4 errors do not occur without the 2 snapshots that I created before running "apt-get dist-upgrade".

root@dcmilphlum173:~# lvs
  LV VG Attr LSize Origin Snap% Move Log Copy% Convert
  datavol vgapp -wi-ao 678.00g
  homevol vgos -wi-ao 1.86g
  rootsnapvol vgos swi-a- 3.00g rootvol 61.85
  rootvol vgos owi-ao 13.97g
  swapvol vgos -wi-ao 7.45g
  tmpvol vgos -wi-ao 1.86g
  varsnapvol vgos swi-a- 2.00g varvol 51.57
  varvol vgos owi-ao 7.45g

Could this be related to the above issue?
I see that the issue from this thread was solved in grub2 (2.02~beta2-9), but the latest version available to precise is the one I have (see below)

root@dcmilphlum173:~# dpkg -l |grep grub
ii grub-common 1.99-21ubuntu3.19 GRand Unified Bootloader (common files)
ii grub-gfxpayload-lists 0.6 GRUB gfxpayload blacklist
ii grub-pc 1.99-21ubuntu3.19 GRand Unified Bootloader, version 2 (PC/BIOS version)
ii grub-pc-bin 1.99-21ubuntu3.19 GRand Unified Bootloader, version 2 (PC/BIOS binaries)
ii grub2-common 1.99-21ubuntu3.19 GRand Unified Bootloader (common files for version 2)

I currently haven't seen any crash or boot failure because of these issues yet, but still I'd like to solve or get around this issue...

1)
Warning: Setting GRUB_TIMEOUT to a non-zero value when GRUB_HIDDEN_TIMEOUT is set is no longer supported.

This warning is because of https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1258597
I was able to solve it by:

function Fix_grub_config() {
  if grep -q "^GRUB_HIDDEN_TIMEOUT=0$" /etc/default/grub || grep -q "^GRUB_HIDDEN_TIMEOUT_QUIET=true$" /etc/default/grub; then
    echo -en "ACTION:\tFixing Grub config... "
    sed -i "s/^GRUB_HIDDEN_TIMEOUT=0$/#GRUB_HIDDEN_TIMEOUT=0/" /etc/default/grub
   sed -i "s/^GRUB_HIDDEN_TIMEOUT_QUIET=true$/#GRUB_HIDDEN_TIMEOUT_QUIET=true/" /etc/default/grub
    echo "Done."
  fi
}

But this fix brings up a new issue for me personally. When running the dist-upgrade, it now shows a pop-up from "grub-pc config", complaining that I modified /etc/default/grub asking me what to do.
As I'm trying to run the dist-upgrade non-interactively, this is a bigger issue for me than the warning, so I will not perform this fix...

2)
rmdir: failed to remove `/var/lib/os-prober/mount': Device or resource busy

By using set -xv I was able to track down this issue a bit further:

/usr/sbin/grub-mkconfig -o /boot/grub/grub.cfg
--> /etc/grub.d/30_os-prober
--> OSPROBED="`os-prober | tr ' ' '^' | paste -s -d ' '`"
--> /usr/bin/os-prober
--> /usr/lib/os-probes/50mounted-tests /dev/sda5

if [ "$mounted" ]; then
                for test in /usr/lib/os-probes/mounted/*; do
                                debug "running subtest $test"
                                if [ -f "$test" ] && [ -x "$test" ]; then
                                                if "$test" "$partition" "$tmpmnt" "$type"; then
                                                                debug "os found by subtest $test"
                                                                if ! umount "$tmpmnt"; then
                                                                                warn "failed to umount $tmpmnt"
                                                                fi
                                                                case "$type" in
                                                                    btrfs)
                                                                                # umount to account for the bind-mount
                                                                                if [ -x "$tmpmnt/@/lib" ] && \
                                                                                   ! umount $tmpmnt; then
                                                                                                warn "failed to umount $tmpmnt"
                                                                                fi
                                                                                ;;
                                                                esac
                                                                rmdir "$tmpmnt" || true
                                                                exit 0
                                                fi
                                fi
                done
                if ! umount "$tmpmnt"; then
                     ...