Debugging live-boot persistence when persistence file is located on same ext4 partition as live ISO (which is booted with GRUB2)

live-boot persistence

# I boot from an ISO that is loop-mounted with GRUB2 like this:
root@debian:/home/user# cat /lib/live/mount/findiso/boot/grub/grub.cfg
# (...)
menuentry "binary.hybrid.iso" {
        insmod ext2
        iso_path="/boot/binary.hybrid.iso"
        export iso_path
        args="findiso=${iso_path} live-config.keyboard-layouts=de live-config.locales=de_DE.UTF-8 live-config.timezone=Europe/Berlin boot=live config quiet splash"
        export args
        loopback loop ${iso_path}
        linux (loop)/live/vmlinuz $args
        initrd (loop)/live/initrd.img
}
# (...)

# When I boot without the "persistence" boot option:
# ==================================================

root@debian:/home/user# cat /etc/*release
PRETTY_NAME="Debian GNU/Linux 7 (wheezy)"
NAME="Debian GNU/Linux"
VERSION_ID="7"
VERSION="7 (wheezy)"
ID=debian
ANSI_COLOR="1;31"
HOME_URL="http://www.debian.org/"
SUPPORT_URL="http://www.debian.org/support/"
BUG_REPORT_URL="http://bugs.debian.org/"

root@debian:/home/user# cat /lib/live/mount/medium/.disk/info 
Debian GNU/Linux 7.0.0 "Wheezy" - Official Snapshot i386 LIVE Binary 20130705-09:20

root@debian:/home/user# dpkg-query -W -f '${status} ${package} ${version}\n' | sed -n 's/^install ok installed //p' | grep live
live-boot 3.0.1-1
live-boot-doc 3.0.1-1
live-boot-initramfs-tools 3.0.1-1
live-config 3.0.23-1
live-config-doc 3.0.23-1
live-config-sysvinit 3.0.23-1
live-manual 1:3.0.2-1
live-manual-epub 1:3.0.2-1
live-manual-html 1:3.0.2-1
live-manual-odf 1:3.0.2-1
live-manual-pdf 1:3.0.2-1
live-manual-txt 1:3.0.2-1
live-tools 3.0.20-1

# This is my persistence file. It is located in the root directory of the ext4 partition 
root@debian:/home/user# ls /lib/live/mount/findiso/persistence 
/lib/live/mount/findiso/persistence
root@debian:/home/user# mount /lib/live/mount/findiso/persistence /mnt/ -oloop,ro
root@debian:/home/user# cat /mnt/persistence.conf 
/etc
/root/persistent

# During boot, I get an error
root@debian:/home/user# cat /var/log/live/boot.log
umount: can't umount /live/overlay: Device or resource busy

# This is what is mounted
root@debian:/home/user# mount
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
udev on /dev type devtmpfs (rw,relatime,size=10240k,nr_inodes=215958,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)
tmpfs on /run type tmpfs (rw,nosuid,noexec,relatime,size=350408k,mode=755)
/dev/sda1 on /lib/live/mount/findiso type ext4 (ro,noatime,user_xattr,barrier=1,data=ordered)
/dev/loop0 on /lib/live/mount/medium type iso9660 (ro,noatime)
/dev/loop1 on /lib/live/mount/rootfs/filesystem.squashfs type squashfs (ro,noatime)
tmpfs on /lib/live/mount/overlay type tmpfs (rw,relatime)
tmpfs on /lib/live/mount/overlay type tmpfs (rw,noatime,mode=755)
aufs on / type aufs (rw,relatime,si=6b210e2a,noxino)
tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k)
tmpfs on /run/shm type tmpfs (rw,nosuid,nodev,noexec,relatime,size=700800k)

# When I boot with the "persistence" boot option:
# ==================================================

root@debian:/home/user# ls /lib/live/mount/findiso/persistence 
ls: cannot access /lib/live/mount/findiso/persistence: No such file or directory

root@debian:/home/user# cat /var/log/live/boot.log
mount: mounting /dev/sda2 on /live/persistence/sda2 failed: No such device
mount: mounting /dev/sda5 on /live/persistence/sda5 failed: No such device
mount: mounting /dev/sda on /live/persistence/sda failed: No such device
mount: mounting /dev/sr0 on /live/persistence/sr0 failed: No such device
cp: can't create directory '/live/persistence/loop2/etc': Read-only file system
mount: mounting /live/persistence/loop2/etc on /root/etc failed: No such file or directory
mkdir: can't create directory '/live/persistence/loop2/root': Read-only file system
cp: can't create directory '/live/persistence/loop2/root/persistent': No such file or directory
mount: mounting /live/persistence/loop2/root/persistent on /root/root/persistent failed: No such file or directory
umount: can't umount /live/overlay: Device or resource busy

root@debian:/home/user# mount
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
udev on /dev type devtmpfs (rw,relatime,size=10240k,nr_inodes=215958,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000)
tmpfs on /run type tmpfs (rw,nosuid,noexec,relatime,size=350408k,mode=755)
/dev/sda1 on /lib/live/mount/persistence/sda1 type ext4 (ro,noatime,user_xattr,barrier=1,data=ordered)
/dev/loop0 on /lib/live/mount/medium type iso9660 (ro,noatime)
/dev/loop1 on /lib/live/mount/rootfs/filesystem.squashfs type squashfs (ro,noatime)
tmpfs on /lib/live/mount/overlay type tmpfs (rw,relatime)
tmpfs on /lib/live/mount/overlay type tmpfs (rw,noatime,mode=755)
aufs on / type aufs (rw,relatime,si=c3e74db7,noxino)
/dev/loop2 on /lib/live/mount/persistence/loop2 type ext4 (ro,noatime,user_xattr,barrier=1,data=ordered)
tmpfs on /run/lock type tmpfs (rw,nosuid,nodev,noexec,relatime,size=5120k)
tmpfs on /run/shm type tmpfs (rw,nosuid,nodev,noexec,relatime,size=700800k)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,nosuid,nodev,noexec,relatime)