remastered 15.10 live usb doesn't find the persistent home medium (casper-rw) and drops to busybox

the short log would be:
___________________________________________________
Begin: Running /scripts/casper-premount ... done.
done.
umount: can't umount /cdrom: Device or resource busy
Warning: Unable to find the persistent home medium
umount: can't umount /cdrom: Device or resource busy
Warning: Impossible to include the casper-sn Snapshot
umount: can't umount /cdrom: Device or resource busy
Warning: Impossible to include the home-sn Snapshot
done.
___________________________________________________

removing the "persistence" keyword from the syslinux.cfg works and the live usb drive boots just fine.
i found older bug reports concerning the same problem but the fix proposed in 2010 is already integrated into the script "casper".

so i started the flashdrive with the casper debug= option and i see the following (after probing several other devices it finally finds the right device and partition (sdb3)

___________________________________________________

+ cow_backing_mp=/cdrom
+ [ -e /cdrom/casper-rw ]
+ umount /cdrom
+ sys2dev /sys/block/sdb/sdb3
+ sysdev=/block/sdb/sdb3
+ udevadm info -q name -p /block/sdb/sdb3
+ echo /dev/sdb3
+ devname=/dev/sdb3
+ /sbin/blkid -s LABEL -o value /dev/sdb3
+ [ casper-rw = casper-rw ]
+ echo /dev/sdb3
+ return
+ cowprobe=/dev/sdb3
+ [ -b /dev/sdb3 ]
+ cowdevice=/dev/sdb3
+ get_fstype /dev/sdb3
+ local FSTYPE
+ local FSSIZE
+ fstype
+ eval FSTYPE=ext4 FSSIZE=8458862592
+ FSTYPE=ext4 FSSIZE=8458862592
+ [ ext4 != unknown ]
+ echo ext4
+ return 0
+ cow_fstype=ext4
+ cow_mountopt=rw,noatime
+ mount -t ext4 -o rw,noatime /dev/sdb3 /cow
+ [ ! -d /cow/upper ]
+ mkdir -p /cow/upper
+ continue
+ continue
+ mkdir -p /cow/work
+ [ -f /cow/format ]
+ [ DEFAULT = DEFAULT ]
+ modprobe -q -b overlay
+ grep -q ^overlay$
+ cut -f2 /proc/filesystems
+ UNIONFS=overlay
+ break
___________________________________________________

this looks fine to me.. it looks like it recognizes everything .. it's ext4 .. label casper-rw.. it's mounting it...

a little bit further down in the loooong log file it states the following:

______________________________________________

+ cow_backing_mp=/home-rw-backing
+ [ -e /home-rw-backing/home-rw ]
+ umount /home-rw-backing
+ sys2dev /sys/block/sdb/sdb3
+ sysdev=/block/sdb/sdb3
+ udevadm info -q name -p /block/sdb/sdb3
+ echo /dev/sdb3
+ devname=/dev/sdb3
+ /sbin/blkid -s LABEL -o value /dev/sdb3
+ [ casper-rw = home-rw ]
+ get_fstype /dev/sdb3
+ local FSTYPE
+ local FSSIZE
+ fstype
+ eval FSTYPE=ext4 FSSIZE=8458862592
+ FSTYPE=ext4 FSSIZE=8458862592
+ [ ext4 != unknown ]
+ echo ext4
+ return 0
+ [ ext4 = vfat ]
+ homecow=
+ [ -b ]
+ [ n != y ]
+ log_warning_msg Unable to find the persistent home medium
+ _log_msg Warning: Unable to find the persistent home medium\n
+ [ n = y ]
+ printf Warning: Unable to find the persistent home medium\n
Warning: Unable to find the persistent home medium
__________________________________________________________

so what's the problem here??

i am using kubuntu 15.10 beta on my system (syslinux install is also broken but that's something for a bug report)
i created a iso out of my system by using the distroshare ubuntu-imager script which i altered to create a ubuntu startdisc creator conform hybrid iso that supports syslinux ..

this is probably due to the remastering process but since i changed nothing within the casper scripts and everything works very well except the "persistens" thing.. it's probably a bug ??